(COD)

Multinational Agribusiness Systems Incorporated

PARAGUAY

MINIFUNDIA CROP INTENSIFICATION

PROJECT

FROST PROTECTION REPORT

USAIDCREDICOOPMASI

Work performed under contract LAC-0118-C-00-1026-00

July 30 1982

Multinational Agribusiness Systems Incorporated

1901 N Fort Myer Dr 307 Arlington VA 22209-1640

Telephone (703) 527-4300

Cable MASIGRUUP Arlington VA

Telex 64814 MASI UW via WUI

Project Dircctor Walter A Price

Report prepared by

Robert F Brewer Frost Protection Specialist

CONTENTS

Page

I INTRODUCTION 1

II CULTURAL PRACTICES 2

III AVAILABLE RESOURCES FOR FROST PROTECTION 6

IV PRINCIPLES AND TECHNIQUES OF FROST PROTECTION 7

A Advective Freeze 7 B Radiation Frost 7 C Inversion 8 D Radiation 8 E Phase Change of Water 9 F Phase Rule 9 G Evaporation - Condensation 10 H Freezing - Thawing - Sublimation 11 I Air Dams and Windbreaks 11

V TECHNIQUES FOR PROVIDING FROST PROTECTION 12

A Site Selection and Exposure 12 B Covering Plants 3 C Active Measures for Frost Protection 14

VI SPECIFIC RECOMMENDATIONS FOR MINIFUNDIA CROPS 22

A Tomatoes 22 B Bananas 26 C Pineapples 29 D Strawberries 30

VII SUGGESTIONS FOR FIELD TESTS AND RESEARCH 30

VIIISUGGESTIONS FOR AUDIO-VISUAL AIDS 32

I INTRODUCTION

The Minifundia Crop Intensification Project is a cooperative effort

by USAID (US Agency for International Development) and CREDICOOP

a private cooperative to provide technical assistance and production

credit to small farmers in the minifundia (small farm) area of

central Paraguay The purpose of this project is to help these

small farmers apply modern technology to farming and to develop

markets for new cash crops so that they will be encouraged to divershy

sify and intensify crop production Four high value cash crops

tomatoes pineapple strawberry and banana were chosen as promising

replacements for the traditional cotton tobacco and soybeans

formerly grown

One primary requirement for a stable market is a dependable supply

year after year Any factor which interferes with a dependable

supply on a regular basis placs the whole system in jeopardy One

such factor ini the production and marketing of cold sensitive crops

is frost damage Once a market is lost due to inability to meet

Qemand considerable difficulty may be experienced in regaining the

market It is imperative therefore that crop failure due to cold

damage be kept to a minimum

Most of the minifundia plots (potentially approximately 600) are

located within a 200 km circumference of Asuncion Frosts occur

in all districts somewhat more often (three nights per year) in

the southern districts near San Juan Bautista than in the central

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area (Caacupe and Col Oviedo) which averages approximately one night

of frost per year according to official government meteorological

recc Js It should be mentioned that such measurements are often

made in or near urban areas which can be several degrees warmer than

remote rural areas covered with vegetation

Figure 1 shows the location of participating cooperatives and the

cash crops being grown in the various areas Planting in the

circled areas were personally visited by the MASI Frost Protection

Specialist

II Cultural Practices Resources

A Tomatoes

Two varieties of tomatoes are raised for the Buenos Aires early

market The current practice is to plant double rows on contour

terraces perpendicular to the principal slope The vines are

trained on X-shaped stakes which meet approximately 15 m above

the ground Irrigation is provided by hoeing out a shallow

basin between two opposing vines which can be filled with water

All of the plots which vary in size from a minimum of 14 ha

to a maximum of 34 ha are supplied centrifugal pumps capable

of pumping 100 liters of water per minute at an altitude of 50

meters--slightly more at lower less at higher elevations The

------

-3-

N

FIGURE 1

Location of CREDICOOP Miniftuidia Plots

a

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COMCEPUNM

SAMl PEUD ~

A=-cyrs y Eztleroc

- Caraiaa

Reemby

vileta -GCRA

lentoa

PIA

- Ma s

~T t5F ~qC 10

- 4 shy

water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

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Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

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not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

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settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

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(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

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sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

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H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

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hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

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2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

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because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

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1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

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Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

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plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

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this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

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Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

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absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

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areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

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materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

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coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

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4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

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just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

PARAGUAY

MINIFUNDIA CROP INTENSIFICATION

PROJECT

FROST PROTECTION REPORT

USAIDCREDICOOPMASI

Work performed under contract LAC-0118-C-00-1026-00

July 30 1982

Multinational Agribusiness Systems Incorporated

1901 N Fort Myer Dr 307 Arlington VA 22209-1640

Telephone (703) 527-4300

Cable MASIGRUUP Arlington VA

Telex 64814 MASI UW via WUI

Project Dircctor Walter A Price

Report prepared by

Robert F Brewer Frost Protection Specialist

CONTENTS

Page

I INTRODUCTION 1

II CULTURAL PRACTICES 2

III AVAILABLE RESOURCES FOR FROST PROTECTION 6

IV PRINCIPLES AND TECHNIQUES OF FROST PROTECTION 7

A Advective Freeze 7 B Radiation Frost 7 C Inversion 8 D Radiation 8 E Phase Change of Water 9 F Phase Rule 9 G Evaporation - Condensation 10 H Freezing - Thawing - Sublimation 11 I Air Dams and Windbreaks 11

V TECHNIQUES FOR PROVIDING FROST PROTECTION 12

A Site Selection and Exposure 12 B Covering Plants 3 C Active Measures for Frost Protection 14

VI SPECIFIC RECOMMENDATIONS FOR MINIFUNDIA CROPS 22

A Tomatoes 22 B Bananas 26 C Pineapples 29 D Strawberries 30

VII SUGGESTIONS FOR FIELD TESTS AND RESEARCH 30

VIIISUGGESTIONS FOR AUDIO-VISUAL AIDS 32

I INTRODUCTION

The Minifundia Crop Intensification Project is a cooperative effort

by USAID (US Agency for International Development) and CREDICOOP

a private cooperative to provide technical assistance and production

credit to small farmers in the minifundia (small farm) area of

central Paraguay The purpose of this project is to help these

small farmers apply modern technology to farming and to develop

markets for new cash crops so that they will be encouraged to divershy

sify and intensify crop production Four high value cash crops

tomatoes pineapple strawberry and banana were chosen as promising

replacements for the traditional cotton tobacco and soybeans

formerly grown

One primary requirement for a stable market is a dependable supply

year after year Any factor which interferes with a dependable

supply on a regular basis placs the whole system in jeopardy One

such factor ini the production and marketing of cold sensitive crops

is frost damage Once a market is lost due to inability to meet

Qemand considerable difficulty may be experienced in regaining the

market It is imperative therefore that crop failure due to cold

damage be kept to a minimum

Most of the minifundia plots (potentially approximately 600) are

located within a 200 km circumference of Asuncion Frosts occur

in all districts somewhat more often (three nights per year) in

the southern districts near San Juan Bautista than in the central

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area (Caacupe and Col Oviedo) which averages approximately one night

of frost per year according to official government meteorological

recc Js It should be mentioned that such measurements are often

made in or near urban areas which can be several degrees warmer than

remote rural areas covered with vegetation

Figure 1 shows the location of participating cooperatives and the

cash crops being grown in the various areas Planting in the

circled areas were personally visited by the MASI Frost Protection

Specialist

II Cultural Practices Resources

A Tomatoes

Two varieties of tomatoes are raised for the Buenos Aires early

market The current practice is to plant double rows on contour

terraces perpendicular to the principal slope The vines are

trained on X-shaped stakes which meet approximately 15 m above

the ground Irrigation is provided by hoeing out a shallow

basin between two opposing vines which can be filled with water

All of the plots which vary in size from a minimum of 14 ha

to a maximum of 34 ha are supplied centrifugal pumps capable

of pumping 100 liters of water per minute at an altitude of 50

meters--slightly more at lower less at higher elevations The

------

-3-

N

FIGURE 1

Location of CREDICOOP Miniftuidia Plots

a

CC

e-en

COMCEPUNM

SAMl PEUD ~

A=-cyrs y Eztleroc

- Caraiaa

Reemby

vileta -GCRA

lentoa

PIA

- Ma s

~T t5F ~qC 10

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water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

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Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

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not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

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Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

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settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

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(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

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sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

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H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

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hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

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2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

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because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

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1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

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Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

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plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

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this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

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Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

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absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

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areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

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materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

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coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

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4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

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just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

CONTENTS

Page

I INTRODUCTION 1

II CULTURAL PRACTICES 2

III AVAILABLE RESOURCES FOR FROST PROTECTION 6

IV PRINCIPLES AND TECHNIQUES OF FROST PROTECTION 7

A Advective Freeze 7 B Radiation Frost 7 C Inversion 8 D Radiation 8 E Phase Change of Water 9 F Phase Rule 9 G Evaporation - Condensation 10 H Freezing - Thawing - Sublimation 11 I Air Dams and Windbreaks 11

V TECHNIQUES FOR PROVIDING FROST PROTECTION 12

A Site Selection and Exposure 12 B Covering Plants 3 C Active Measures for Frost Protection 14

VI SPECIFIC RECOMMENDATIONS FOR MINIFUNDIA CROPS 22

A Tomatoes 22 B Bananas 26 C Pineapples 29 D Strawberries 30

VII SUGGESTIONS FOR FIELD TESTS AND RESEARCH 30

VIIISUGGESTIONS FOR AUDIO-VISUAL AIDS 32

I INTRODUCTION

The Minifundia Crop Intensification Project is a cooperative effort

by USAID (US Agency for International Development) and CREDICOOP

a private cooperative to provide technical assistance and production

credit to small farmers in the minifundia (small farm) area of

central Paraguay The purpose of this project is to help these

small farmers apply modern technology to farming and to develop

markets for new cash crops so that they will be encouraged to divershy

sify and intensify crop production Four high value cash crops

tomatoes pineapple strawberry and banana were chosen as promising

replacements for the traditional cotton tobacco and soybeans

formerly grown

One primary requirement for a stable market is a dependable supply

year after year Any factor which interferes with a dependable

supply on a regular basis placs the whole system in jeopardy One

such factor ini the production and marketing of cold sensitive crops

is frost damage Once a market is lost due to inability to meet

Qemand considerable difficulty may be experienced in regaining the

market It is imperative therefore that crop failure due to cold

damage be kept to a minimum

Most of the minifundia plots (potentially approximately 600) are

located within a 200 km circumference of Asuncion Frosts occur

in all districts somewhat more often (three nights per year) in

the southern districts near San Juan Bautista than in the central

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area (Caacupe and Col Oviedo) which averages approximately one night

of frost per year according to official government meteorological

recc Js It should be mentioned that such measurements are often

made in or near urban areas which can be several degrees warmer than

remote rural areas covered with vegetation

Figure 1 shows the location of participating cooperatives and the

cash crops being grown in the various areas Planting in the

circled areas were personally visited by the MASI Frost Protection

Specialist

II Cultural Practices Resources

A Tomatoes

Two varieties of tomatoes are raised for the Buenos Aires early

market The current practice is to plant double rows on contour

terraces perpendicular to the principal slope The vines are

trained on X-shaped stakes which meet approximately 15 m above

the ground Irrigation is provided by hoeing out a shallow

basin between two opposing vines which can be filled with water

All of the plots which vary in size from a minimum of 14 ha

to a maximum of 34 ha are supplied centrifugal pumps capable

of pumping 100 liters of water per minute at an altitude of 50

meters--slightly more at lower less at higher elevations The

------

-3-

N

FIGURE 1

Location of CREDICOOP Miniftuidia Plots

a

CC

e-en

COMCEPUNM

SAMl PEUD ~

A=-cyrs y Eztleroc

- Caraiaa

Reemby

vileta -GCRA

lentoa

PIA

- Ma s

~T t5F ~qC 10

- 4 shy

water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

- 5 -

Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

I INTRODUCTION

The Minifundia Crop Intensification Project is a cooperative effort

by USAID (US Agency for International Development) and CREDICOOP

a private cooperative to provide technical assistance and production

credit to small farmers in the minifundia (small farm) area of

central Paraguay The purpose of this project is to help these

small farmers apply modern technology to farming and to develop

markets for new cash crops so that they will be encouraged to divershy

sify and intensify crop production Four high value cash crops

tomatoes pineapple strawberry and banana were chosen as promising

replacements for the traditional cotton tobacco and soybeans

formerly grown

One primary requirement for a stable market is a dependable supply

year after year Any factor which interferes with a dependable

supply on a regular basis placs the whole system in jeopardy One

such factor ini the production and marketing of cold sensitive crops

is frost damage Once a market is lost due to inability to meet

Qemand considerable difficulty may be experienced in regaining the

market It is imperative therefore that crop failure due to cold

damage be kept to a minimum

Most of the minifundia plots (potentially approximately 600) are

located within a 200 km circumference of Asuncion Frosts occur

in all districts somewhat more often (three nights per year) in

the southern districts near San Juan Bautista than in the central

- 2 shy

area (Caacupe and Col Oviedo) which averages approximately one night

of frost per year according to official government meteorological

recc Js It should be mentioned that such measurements are often

made in or near urban areas which can be several degrees warmer than

remote rural areas covered with vegetation

Figure 1 shows the location of participating cooperatives and the

cash crops being grown in the various areas Planting in the

circled areas were personally visited by the MASI Frost Protection

Specialist

II Cultural Practices Resources

A Tomatoes

Two varieties of tomatoes are raised for the Buenos Aires early

market The current practice is to plant double rows on contour

terraces perpendicular to the principal slope The vines are

trained on X-shaped stakes which meet approximately 15 m above

the ground Irrigation is provided by hoeing out a shallow

basin between two opposing vines which can be filled with water

All of the plots which vary in size from a minimum of 14 ha

to a maximum of 34 ha are supplied centrifugal pumps capable

of pumping 100 liters of water per minute at an altitude of 50

meters--slightly more at lower less at higher elevations The

------

-3-

N

FIGURE 1

Location of CREDICOOP Miniftuidia Plots

a

CC

e-en

COMCEPUNM

SAMl PEUD ~

A=-cyrs y Eztleroc

- Caraiaa

Reemby

vileta -GCRA

lentoa

PIA

- Ma s

~T t5F ~qC 10

- 4 shy

water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

- 5 -

Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 2 shy

area (Caacupe and Col Oviedo) which averages approximately one night

of frost per year according to official government meteorological

recc Js It should be mentioned that such measurements are often

made in or near urban areas which can be several degrees warmer than

remote rural areas covered with vegetation

Figure 1 shows the location of participating cooperatives and the

cash crops being grown in the various areas Planting in the

circled areas were personally visited by the MASI Frost Protection

Specialist

II Cultural Practices Resources

A Tomatoes

Two varieties of tomatoes are raised for the Buenos Aires early

market The current practice is to plant double rows on contour

terraces perpendicular to the principal slope The vines are

trained on X-shaped stakes which meet approximately 15 m above

the ground Irrigation is provided by hoeing out a shallow

basin between two opposing vines which can be filled with water

All of the plots which vary in size from a minimum of 14 ha

to a maximum of 34 ha are supplied centrifugal pumps capable

of pumping 100 liters of water per minute at an altitude of 50

meters--slightly more at lower less at higher elevations The

------

-3-

N

FIGURE 1

Location of CREDICOOP Miniftuidia Plots

a

CC

e-en

COMCEPUNM

SAMl PEUD ~

A=-cyrs y Eztleroc

- Caraiaa

Reemby

vileta -GCRA

lentoa

PIA

- Ma s

~T t5F ~qC 10

- 4 shy

water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

- 5 -

Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

------

-3-

N

FIGURE 1

Location of CREDICOOP Miniftuidia Plots

a

CC

e-en

COMCEPUNM

SAMl PEUD ~

A=-cyrs y Eztleroc

- Caraiaa

Reemby

vileta -GCRA

lentoa

PIA

- Ma s

~T t5F ~qC 10

- 4 shy

water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

- 5 -

Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 4 shy

water is delivered to the plots through 1-14 inch (32 mm) poly

pipe and distributed to the individual basins by flexible garden

hose The maximum distance of flow from pump to plot has been

set at 1 km the maximum elevation difference 50 m

Cold protection is presently being attempted by planting the

tomatoes on sloping land (although the slope is often to the

south instead of north) and providing 25 cm wide by 50 cm deep

holes dug in the ground in which coconut husk (a waste product

of palm oil production) will be burned in the advent of potential

frost Evidently the idea is to produce copious smoke which will

cover and thereby protect the tomatoes Unfortunately this

approach is not apt to produce any beneficial results for reasons

which will be discussed later

B Bananas

Two types of bananas are grown in the area the shorter Cavendish

type and the taller smaller fruited Indian-type Mysore variety

The Cavendish is considered more cold-sensitive and is therefore

grown on higher ground and steeper slopes than the Mysore Most

of the banana plantings visited (see Fig 1) were on relatively

high ground although several plantings were hemmed in by shrubs

and trees which would interifere with cold air drainage All

of the plantings were clean cultivated but in several instances

corn stalks and old banana leaves were being used as mulch to

conserve moisture and help prevent erosion Unfortunately such

materials increase frost hazard

- 5 -

Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 5 -

Several of the plantings showed widespread symptoms of potassium

deficiency and some plants had succumbed to nematode attack

Except for site selection no provision for frost protection had

been made except that one grower had covered nearly mature bunches

with old lime bags for cold protection of the bunches Dr Jordan

is distributing blue polyethylene sheaths on an experimental

basis for the same purpose Banana fruit is subject to cold

injury to developing fruit at temperatures far above freezing

therefore the special c icern for the fruit bunches

C Pineapple

The two cooperating minifundia pineapple plots visited were

relatively small (14 ha or less) and were grown without benefit

of supplementary irrigation One plot was very weedy the other

was suffering from nematodes and nutrient deficiencies Both

plots were on relatively flat ground hemmed in by bananas on the

downslope side

D Strawberries

Only two plantings of strawberries were visited experimental

plots at the National Institute of Agronomy (IAN) and another

experimental planting on peatbog land near Ypacaral Figure 1

taken from a 1979 USAID report shows strawberries then being

grown near Neemby Villeta and Yaguar6n all just south of

Asunci6n Cultural practices at these latter locations could

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 6 shy

not be ascertained but the IAN and Ypacarai plantings were on

raised beds Water for irrigation was available at both sites

pressurized at the experimental farm and in a gravity ditch at

Ypacarai The IAN plots involved comparisons of varieties

conventional and drip irrigation in well-designed experiments

The bog planting at Ypacaral was partially mulched with straw

to keep the berries off the damp ground

III Available Resources for Frost Protection

Most of the plantings visited depended solely on site selection

(high or sloping ground) for protection Many of the tomato plots

particularly in the colder southern areas were on south rather

than north-facing slopes In some cases distance up the slope

was dictated by the 1 km reach of the irrigation pump

All tomato plots are equipped with pumped water for irrigation

but all plots regardless of size had the same pump capacity (100

litersminute) The ditches and ponds from which some of the pumps

received their water supply appeared somewhat limited in capacity

to provide the 100 liters per minute for an extended period (10 to

14 hours)

Many of the plots were partially surrounded by brush woods thaic

could be cleared and the brush used as a source of firewood in the

event of a particularly cold period of short duration

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 7 -

Current recommended cultural practices for growing tomatoes include

the application of copper and antibiotic sprays for disease control

More frequent applications might increase cold tolerance

IV Principles and Techniques for Providing Frost Protection

Before making specific recommendations it might be well to summarize

the basic principles involved and define a few terms as they apply

to frost protection

A Advective Freeze

An advective freeze is caused by sub-freezing air being blown

in from somewhere else This type of damaging cold is usually

associated with the passage of storm fronts there is usually

little or no inversion and there may be some cloudiness

B Radiation Frost

Unlike the freeze first described a frost is due to locally

developed cold produced by direct radiation of heat by exposed

plant parts or by contact with cold air which has been chilled

by other radiating surfaces Plant foliage exposed to the sky

on a clear calm night will be several degrees colder than the

surrounding air and therefore will pull heat out of this air

causing it to cool become heavier and move downward Cold air

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 8 shy

settling to the ground will be rewarmed and sent aloft again

to warm the foliage so long as the soil surface is warmer than

the air When soil heat accumulated the previous day is used

up the subsiding cold air is not rewarmed and therefore accumushy

lates if the terrain is flator it flows downhill to lower ground

if there is a slope So long as there is unlimited and unreshy

stricted downward flow of the cold air plants in elevated locashy

tions remain above the cold air If the slope is limited or

the catchbasin nearby is relatively limited in size the cold

air will eventually fill the basin and work its way up the

slopes mur-h as water does when it fills the area behind a dam

eventually reaching the crops planted on these slopes Frost

conditions require clear skies and little or no wind

C Inversion

The presence of cold air near the ground with warmer air aloft

is called an inversion The warm air is actually sandwiched

between even colder air farther aloft and the cold air on the

grounid Absence of wind which would break up the layering is

necessary for the development of inversions

D Radiation

Sensible heat is the result of atomic oscillation--the greater

the heat the greater the oscillation Like other energy (light

sound radiowaves) heat is radiated or sent out in wave form

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 9 shy

(infrared) from a body of higher energy content (hotter) to one

of lower content (colder) Heat will therefore move from a

relatively warm leaf or soil surface toward the very cold outer

atmosphere on a clear calm night The presence of excess water

droplets (clouds or fog) in the atmosphere will greatly reduce

this process because water droplets absorb the out-going radiashy

tion and re-radiate it back toward the earth thereby acting

somewhat like a mirror Some radiation (20 to 30 percent) does

get through even a heavy cloud layer however but the reflected

portion together with the heat stored in the soil is usually

sufficient to prevent nocturnal chilling to damaging temperatures

E Phase Changes of Water

Water the basis of all life on earth is a remarkable substance

It is one of the few substances having a higher specific density

in the liquid phase (water) than in the solid phase (ice) Thereshy

fore ice freezes on top of water and organisms below are protected

At the freezing point of water (O C at atmospheric pressure) all

three phases of water can exist--vapor liquid and solid

F Phase Rule

So long as the liquid and solid phases (water and ice) exist

together the temperature of the mixture will not go below the

freezing point (O C) This is of great importance when overhead

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 10 shy

sprinkling is used to protect tender plants or buds Keeping a

water-ice mixture on the cold-sensitive plant parts guarantees

a temperature no lower than 00 C Should application of water

cease or rate of freezing exceed rate of application so that

hoses and nozzles freeze only the solid form (ice) remains and

its temperature can plunge far below freezing especially under

dry windy conditions

G Evaporation - Condensation

An extremely important property of water is the relatively large

(540 calories per gram) auDunt of heat required to change liquid

water to vapor So far as frost protection is concerned of

equal importance is that the same amount of heat is released

when water vapor condenses to a liquid Any time a plant surshy

face is colder than the dewpoint of surrounding air moisture

will condense on that foliage with attendant release of heat in

the process

Sprinkling leaves with water on cold dry nights (dewpoint below

critical plant temperature) can lower temperatures and increase

damage due to the reverse process evaporation of moisture from

the leaf surface a process which absorbs heat from the surroundshy

ings thereby cooling them

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 11 -

H Freezing - Thawing - Sublimation

deg When liquid water at O C changes to ice at 00 80 calories are

released per gram Liquid water cooling from 200 C to water at

00 C only releases 20 calories in the process but if it actually

freezes five times this amount or a total of 100 calories is

released The same amount of heat must be added to reverse the

process 80 calories per gram to melt one gram of ice

Should the relative humidity be low however it is possible for

a solid such as ice to sublime or go directly from the solid to

the vapor phase When this happens very large amounts of energy

(620 calories per gram) are absorbed This enters the frost

protection picture when overhead sprinkling is attempted on a

cold windy night with dew points below the critical injury

temperature and the water flow stops for some reason

I Air Dams and Windbreaks

Thickly planted tall vegetation adjacent to an agricultural

planting can be beneficial or detrimental If upwind and upslope

they can afford protection from chilling winds or divert downshy

slope drift of cold air from strong radiating surfaces above

Air flowing downslope from dense ground covers such as alfalfa

or dense pasture grass can be 2 to 40 colder than air draining

off of cleared land that is firm and moist A - or shaped

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 12 shy

hedgerow windbreak above the planting w4ll send the cold air to

the side or sides A windbreak below a tender crop planting

can be damaging because it will act as a dam interfering with

the downslope movement of cold air off of the crop

V Techniques for Providing Frost Protection - Passive Measures

A Site Selection and Exposure

The best frost protection is planting in a frost-free site

Much of the damage and many of the cold-related problems could

be avoided by more attention to siting Although there is no

substitute for experience regarding performance of a particular

site during a genera frost attention to a few basic rules will

always help

i When possible locate early planted frost-sensitive crops on

slopes getting maximum exposure to the sun during the short

days of winter In the southern hemisphere this is a north

or northwest-facing slope In central Paraguay cold winds

come up from the south so crops on north-facing slopes will

be less exposed to chilling winds and therefore advective

freezing Maximum daytime exposure assures maximum soil

heating--the principal source of heat during the night Since

hilltops are more exposed to chilling winds side slopes are

usually somewhat better affording good air drainage as well

as shelter

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 13 shy

2 Plant on the warmest soil available Heavier silt and loam

soils generally retain more heat at night than do light

sandy soils Where possible avoid coarse sandy soils or

dry peat soils Keep soils firm moist and clear of weeds

Firm moist clean cultivated bare soils absorb and store

more heat during the day and therefore can release more heat

at niaht Recently cultivated or otherwise loose soils do

not conduct absorbed heat to the surface as well as compacted

soils Moist soils will store and then release nearly twice

as much heat as dry soil of the same type

3 Pay attention to surrounding vegetation and land use both

above and below the frost-sensitive planting Upslope land

covered with dense vegetation sheds colder air than cleanshy

cultivated or sparsely covered land Dense tall plantings

below the planting can act as a dam preventing the off-flow

of cold air as mentioned previously Windbreaks erected or

planted above the site can be used to sidetrack or hold back

unwanted cold air but avoiding it altogether by avoidance

or clearing is preferable

B Covering Plants for Cold Protection

Covering plants is one of the oldest and most dependable means

of providing protection from freezing or frost Insulating

materials such as (orn stalks palm fronds reed mats burlap

or even kraft paper provide a large degree of cold protection

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 14 shy

because they interrupt the outflow of heat from the plant If

no heat is lost the temperature will not go down--a simple but

basic rule

Covering with plastic is sometimes effective sometimes not

Ordinary clear vinyl and polyethylene sheeting is not a good

insulator with a film of moisture it becomes a fairly good heat

shield

Any poor heat conductor between the crop and the open sky affords

some protection Sensitive plants grown under or partially under

taller plants will receive some protection against radiation

heat loss

C Active Measures for Frost Protection

Sometimes in spite of careful site selection good soil preparashy

tion and air drainage and even covering to cut down heat loss

temperatures reach or drop below those considered critical for

economic plant growth If this happens very often the only way

such a crop can continue to be grown in a dependable manner is

to provide some means for adding heat to make up for the excess

which is lost or to modify the crop in such a way that it will

tolerate lower than otherwise damaging temperatures

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 15 shy

1 Heaters

Fire especially burning petroleum products is a dependable

but very expensive means of replacing lost heat Wood fires

are also effective if sufficient fuel is on hand to maintain

them throughout the frost period Table 2 contains a listing

of common fuels together with the amount of heat to be

expected When using fires of any type it is important to

use many small fires instead of a few big ones The latter

waste most of the heat because the flames and heat updraft

break through the inversion layer Many years of trials and

research with oil-fired orhnard heaters consuming approxishy

mately 4 liters of fuel per heater per hour have shown that

to provide protection to -5 or -60 C approximately 100 heaters

per ha are required representing an expenditure of approxishy

mately $100 per ha per hour in the USA (approximately $400

per hour in Paraguay) These heaters will provide approxishy

mately 3400000 Kcal or about three times the theoretical

amount being lost per hour from a hectare of land Needless

co say economics rule out the use of oil heaters for extended

periods except in the case of very expensive nursery stock

or non-replaceable specimens

2 Water

Where available pumped well water has replaced oil-burning

heaters as a source of replacement heat in the USA for

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 16 -

Table 2

HEAT CONTENT OF VARIOUS FUELS

FUEL Heat Released per kg of Fuel

Wood 2500 Kcal

Oil 10000

Coal 7400

Peat 3000

Tires approx 7000

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 17 shy

plantings of vegetables trees and vine- Approximately

400 liters per minute per hectare of well water at a temperashy

ture of 15 to 179 C can be expected to protect row crops

down to a temperature of approximately -20 C on a clear

calm night providing there is good air drainage The 100

liters per minute output of the minifundia pumps is thereshy

fore sufficient for approximately 14 ha Water run in

furrows alongside of or beneath a crop continues to release

heat so long as it is running and there is no film of ice

Shortruns of 2 or 50 meters are therefore better than long

runs which are apt to freeze over Power consumption is

approximately 5 hp per ha

3 Mechanical Mixing

One of the primary characteristics of a radiation frost is

the layering of warm over cold air known as an inversion

In hilly terrains under calm conditions air at 15 meters may

be as much as 50 C warmer than air at 1 meter and 80 C

warmer than air at 5 cm Mechanical mixing of the warmer

air from up above with the colder ground level air results

in a mixture which is midway in temperature between the

extremes Wind machines powered by electrical gasoline or

diesel motors are used to accomplish the mixing Approxishy

mately 25 horsepower is required per ha in multiple instalshy

lations on 16 or mor- ha Small plots of the size used in

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 18 shy

this program would probably require twice as much power

per unit area or 10 to 12 horsepower per 14 or 12 ha plot

This is also obviously out of the question in Paraguay under

present economic circumstances

4 Overhead Sprinkling

Because of the Phase Rule (the temperature of a mixture of

water and ice will not go below 00 C) overhead sprinkling

can be an extremely effective device for providing frost

protection It is also one of the most prone to disaster

if one or more things go wrong So long as sufficient water

is applied to prevent an accumulation of ice there is little

potential for damage but if due to lowering temperatures

or diminished water flow ice formation accelerates serious

injury can result due to the weight of the ice bearing on

the plant Fragile plants such as staked tomatoes are espeshy

cially vulnerable to ice damage Low lying or tough plants

like strawberries or pineapples are less susceptible

Deciduous fruit trees such as apples or pears which are pruned

to support heavy loads are se]dom injured by the ice load when

overhead sprinkled during the cold-sensitive bloom period

Evergreen trees such as citrus or avocadoes on the other hand

can be severely damaged by ice loads

A potential hazard even more damaging than ice load damage

are the consequences of equipment failure during sprinkling

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 19 -

Should the pump stop even for 10 or 20 minutes or the disshy

tribution line burst or the sprinkler stop turning there

will no longer be a mixture of ice and water but just ice

alone The temperature can plummet often to several degrees

below that which would have occurred without any protective

measures This is especially true for breezy low humidity

nights when sublimation of the ice can draw large amounts of

heat out of the sprinkled vegetation

A third potential problem associated with overhead sprinkling

especially during extended cold periods is the flooding or

ponding of excess water applied for frost protection This

can be a serious problem with a crop such as tomatoes which

must be pruned tied or picked on a regular basis Excess

moisture resulting from such sprinkling also increases probshy

lems associated with many disease organisms Erosion can

also be a problem especially on hillsides but provision

can be made to minimize this

5 Artificial Fog

Many attempts have been made to utilize the heat-reflecting

properties of fog Fog or clouds is a suspension of water

droplets in the air Because stable fog droplets are of

approximately the same diameter as the wavelength of infrared

radiation (10 to 30 microns)they are especially effective in

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 20 shy

absorbing heat escaping from the ground and reradiating a

large percentage of it back Smoke particles on the other

hand although very effective in blocking visible light are

too small to absorb the long wave heat radiations f-om soil

and vegetation Whatever success smoke has had when used

for crop protection can be attributed to the moisture dropshy

lets (steam) in the smoke not the carbonaceous particles

themselves Oil smoke generators used in World War II to

hide military installations and ships were found worthless

for preventing frost Burning old tires also produces large

amounts of black smoke but when distributed throughout a

planting releases large amounts of heat over a prolonged

period In this case it is the heat and not the smoke which

is beneficial

Artificial fog or clouds can be produced by atomizing water

at high pressure through 10 to 20 micron orifices or by

condensing steam produced by heating water Piling wet

green foliage or moist stable manure on a well-developed fire

is an age-old system for producing copious amounts of steam

Unfortunately artificially produced fog is not very stable

and tends to move with prevailing air currents therefore

the supply must be continuous during the frost period

Mechanical fog-generating systems are available on the market

but they cost a minimum of $30000 and are best adapted to

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 21 shy

areas of 40 ha or more Cost of operation is minimal once

the capital costs of installation arr- met but again such

systems are not applicable to minifundia operations

6 Antibacterial and Anti-nucleation Treatments

Dr Stephen Lindow in the Department of Plant Pathology at

University of California Berkeley has developed a large

amount of evidence that one of the primary differences between

frost-sensitive and frost-tolerant species is the presence

of a particular type of bacteria on the surface of the former

These bacteria happen to be the ideal size to nucleate ice

formation In their absence fruit and foliage will supershy

cool several degrees below their usual freezing point

Unfortunately due to a lack of sufficient cold weather (only

one night of frost in three years) this approach to frost

protection has not been adequately tested under field condishy

tions Artificial exposure of detached branches or fruit

to cold in a freezer is no substitute for comprehensive field

tests Nevertheless the technique shows promise and with a

crop such as tomatoes which is sprayed regularly with antishy

biotics anyway modification of the spray schedule might

provide a measure of frost tolerance and therefore protection

Materials found effective in reducing nucleating bacteria

counts on citrus in California include Bordeaux Kocide a

Etreptomycin-Terramycin mixture and several anti-nucleation

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 22 shy

materials including ascorbic and phosphoric acids The

antibacterial material must be applied at frequent intervals

to keep bacterial counrs low and is most effective for a week

to ten days after application Anti-nucleation materials must

be applied not more than 48 hours prior to an expected frost

VI Specific Recommendations for Minifundia Crops

A Tomatoes

The following recommendations are based on personal observations

of many plantings but may or may not be applicable in all inshy

stances Special circumstances or considerations may preclude

implementing all approaches but since the effects are generally

additive putting several or most into effect should prove beneshy

ficial

1 Site Locatic and Exposure

Many of the plots visited were on south-facing slopes others

were dangerousiy near the base of the slope and many were

potentially cold due to cold air drainage from surrounding

higher land The potential for damaging frost could be reshy

duced significantly if more attention were paid to site

selection and preparation Where plots were found on colder

south-facing slopes warmer north-facing slopes stood vacant

or covered with brush or a mixture of pasture grass and native

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 23 shy

coconut palms In any case their clearing and reclamation

(most showed signs of once having been farmed) would not be

prohibitively difficult or expensive

2 Clear Upslope Area or Erect Windbreak

Clearing the areas upslope from the tomato plantings would

also reduce frost hazard by reducing the inflow of cold air

developed over pasture and weedy vegetation Where this is

not practical due to different ownership for instance

erection or planting of a protective windbreak on the upwind

side to divert air drainage would be beneficial In some

instances fence rows below the plantings had been allowed to

grow into a hedgerow which could impede air drainage thereshy

fore removal of such obstacles would be beneficial

3 Keep Soil Clean Firm and Moist

Clean firm moist soils absorb the most heat by day and can

furnish the most heat at night Weeds should be removed by

spraying with herbicides or shallow hoeing (not deep cultishy

vation since this loosens the soil and reduces heat transfer

capacity) Keep the soil moist particularly when frosty

weather is expected

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 24 shy

4 Redesign Row Configuration to Facilitate Furrow Irrigation

and Frost Control with Water

If the tomato rows were laid out sloping slightly downgrade

(1 or 20 would be sufficient) a furrow instead of basins

could be constructed under the vines to be used for irrigashy

tion and frost protection Where the grade is somewhat

irregular the furrow could be constructed by connecting the

presently used basins which would serve to slow down flow

rates and assure every plant an adequate supply of water

On a cold night when maximum rate of flow is desired the

connecting troughs could be deeponed where necessary with a

hoe in a matter of a few hours

Running water under the arch made by the opposing tomato

vines should trap most of the available heat contained in

the water The 1-14 inch black poly supply line should be

buried or covered with several inches of soil if water is to

be used for frost protection The small garden hoses should

be kept either drained or coiled and covered because they

will freeze soon after sunset on a frosty night Sloping

the rows slightly downgrade should also improve cold air

drainage out of the planting Some sort of simlplified distrishy

bution system will be needed to provide a steady flow of

water for each furrow A piece of perforated polyethylene

or polyvinyl pipe would suffice or an old barrel with pieces

of 14 inch tubing protruding from holes punched in the sidcs

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 25 shy

just above the bottom This tubing should also be covered

with soil to prevent early freezing

5 Place Insulating Materials over Vines at Night

To further enhance the effects of the irrigation water

lightweight insulating materials such as corn stalks palm

fronds or plastic sheeting could be placed over the tomato

vines particularly on the south which should be the upgrade

side In this ca-P the material could be left one or two

days if more cold weather is expected Such insulation will

provide 1 or 20 C protection by itself and together with

running water underneath should provide protection to -40 C

providing other factors such as air drainage are favorable

6 Burn Wood in Small Fires

Where woody brush is available pile trimmings in small

piles (30 cm diam) among the vines for burning on especially

cold nights Somewhat larger fires can be used along the

updrift side to intercept cold air entering the planting

from above Dumping generous amounts of moist coconut fiber

or other moist green material on established fires might create

enough steamy smoke to be beneficial but maintaining the

fires alone would probably do as much good

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 26 -

Do not start the fires until freezing temperatures are evishy

dent then endeavor to keep them burning slowly until danger

of frost is past--often an hour or more after sunrise

Many small fires are much more beneficial than a few large

ones because this spreads the heat and there is not the

strong updraft which breaks through the inversion and wastes

the heat Instead of burning the coconut husk material in

holes as presently practiced it would be much better to

uurn wood charcoal or other high density materia7s in small

piles or in metal containers such as 10 to 20 liter paint

pails with holes in the sides for ventilation

B Bananas

Bananas are notoriously sensitive to frost a few minutes exposhy

sure to 15 to 20 C being lethal In addition the banana fruit

is subject to cold damage at temperatures well above freezing

With these properties in mind the following recommendations

should minimize cold damage losses

1 Careful Site Selection and P-eparation

Planting sites for bananas should be chosen with extreme care

Since they are a perennial crop the original corm giving

rise to side shoots which replace the original stalk after

fruiting is completed a severe frost not only damages the

- 27 shy

current crop but has a carryover effect on the next crop

Bananas should only be planted on land with good air drainage

preferably on norLn--facing slopes with adequate provision for

cold air flow to lower ground below This is even more critshy

ical for the more frost-sensitive Cavendish type than for the

more tolerant Mysore

Even an otherwise good hillside site can be improved by clearshy

ing uphill areas of brush and grass and getting rid of brush

to improve downhill air drainage On large slopes growing or

erection of windbreaks upslope and to the sides of a banana

planting should help minimize wind damage as well as provide

cold protection

2 Shade with Other Vegetation

A cold-sensitive crop such as banana can be grown under a

canopy of another crop such as palm trees or a sensitive

variety like Cavendish might be grown under the canopy of the

taller more tolerant Mysore Alternate east-west rows of

the two varieties would accomplish this

3 Keep Ground Firm Moist and Free of Weeds

The soil surface is the primary source of heat on a frosty

night Keep the soil firm moist and free of weeds Do not

- 28 shy

cover any significant fraction of the soil with thermal

insulators such as sawdust dry manure corn stalks old

leaves or other mulching materials which would insulate the

soil surface by day and night

4 Cover Bunches with Plastic-Lined Paper

Work with bananas in Australia has shown that covering the

developing fruit bunch with a plastic-lined bag reduced cold

injury provided frost protection and prevented wind and bird

damage to the fruit Perforated plastic was superior to

solid plastic Dr Jordan is currently experimenting with

polyethylene plastic sheaths for protecting bananas

5 Pay Attention to Potassium Nutrition

Many studies have shown a positive relationship between an

adequate potassium supply and frost resistance Banana is

known to require an abundant supply of K for good growth and

production but several plantings visited were obviously

suffering from an inadequate supply Application of potasshy

sium fertilizers to such plantings would undoubtedly improve

growth yields and reduce frost susceptibility

- 29 -

C Pineapple

1 Improved Cultural Practices

The easiest and cheapest way to significantly reduce frost

hazard to the pineapple plots visited would be to do a better

job of weed control and fertilization Better site location

particularly as regards downslope air drainage would also be

beneficial Pineapple like many crops is more sensitive

to frost when deficient in potassium supply Excessive nitroshy

gen applied in the fall can induce a tender flush of growth

which is more susceptible to frost damage but application of

a low-nitrogen high-potassium mixture has been found beneshy

ficial in several areas In Florida generous applications

of chopped tobacco stems were found to provide good nutrition

and increased frost tolerance

2 Covering with Thermal Insulators

Although pineapple can be damaged by exposure to --2 or -30 C

temperatures covering with palm leaves or other shading

greatly increases their frost tolerance In Florida covershy

ing with palmetto fans meadowgrass or lath-type shading

permitted tolerance of temperatures to -50 C Old banana

leaves or palm fronds should make good covering material for

pineapples in Paraguay

- 30 shy

3 Irrigation Water

Where available irrigation water could be used effectively

on pineapple for frost prevention Running water in furrows

between the rows would be the easiest procedure but overshy

head sprinkling would be even more effective providing a

dependable and continuous supply of pressurized water was

available

D Strawberries

The same general recommendations made for pineapple would apply

to strawberries because they are grown in a similar manner

Lightly covering with straw and running water between the rows

would be effective Overhead sprinkling would be very effective

but is subject to the hazards previously discussed (excess water

can be a problem equipment failure or stoppage during operation

can result in severe damage) Some selection for frost resisshy

tance might be effective as it has been in Michigan

VII Suggestions for Field Tests and Research Bearing on Frost

Protection

Application of techniques found effective elsewhere often need

to be modified to meet local needs and limitations Ideas which

look good on paper or in theory do not always live up to

- 31 shy

expectations in the field Before recommending procedures to

the many coops and their member farmers it would be prudent to

first test the proposed procedures under controlled conditions

A few demonstration plotq with cooperating growers or experishy

mental plots at the National Institute of Agronomy (IAN) could

be used to test or demonstrate the following

A Feasibility of interplanting Cavendish (short) and Mysore

(tall) bananas in colder locations to provide frost protecshy

tion by shading for the shorter more frost-sensitive Cavendish

B Tomato variety trial probably at IAN to look for new varieties

combining earliness high quality frost tolerance and resisshy

tance to Septoria and other prevalent diseases

C Influence of potassium supply on growth and frost resistance

of banana could best be tested and demonstrated on one or

more of the potassium-deficient plantings observed in the

field near Oviedo

D Effects of copper and antibiotic sprays on frost tolerance

could be determined by modifying current practices to provide

for frequent applications (2 to 10 day intervals) during

periods of high frost risk (mid-June to mid-August) This

vork should be conducted at the Institute until the benefits

if any as well as the details are worked out

- 32 -

E Procedures for combining shading materials such as palm

fronds with water in furrows under the vines could be worked

out under controlled conditions at IAN and then taken to the

field in the form of demonstration plots A simple procedure

is needed to provide thermal insulation on the south side of

tomato rows using plastic paper or dry vegetation to act as

a radiation shield on frosty nights

VIII Suggestions for Audio-Visual Aids

Since most of the participating farmers cannot read and many cannot

understand Spanish it would serve no good purpose to produce a

printed bulletin or Icaflet of the type used so effectively by the

Extension Service in the United States Instead since one picture

can often convey more information than many words a series of carshy

toon or comic book-like pamphlets or one-page answer sheets could

be produced for distribution through the participating coops If

the original drawings were made bulletin-board size (60 cm x 80 cm)

they could be reproduced as such for illustrated talks photographed

for slide shows and reduced to magazine size for the pamphlets or

answer sheets

Principles and concepts which could be put across in this manner

include the following

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones

- 28 shy

cover any significant fraction of the soil with thermal

insulators such as sawdust dry manure corn stalks old

leaves or other mulching materials which would insulate the

soil surface by day and night

4 Cover Bunches with Plastic-Lined Paper

Work with bananas in Australia has shown that covering the

developing fruit bunch with a plastic-lined bag reduced cold

injury provided frost protection and prevented wind and bird

damage to the fruit Perforated plastic was superior to

solid plastic Dr Jordan is currently experimenting with

polyethylene plastic sheaths for protecting bananas

5 Pay Attention to Potassium Nutrition

Many studies have shown a positive relationship between an

adequate potassium supply and frost resistance Banana is

known to require an abundant supply of K for good growth and

production but several plantings visited were obviously

suffering from an inadequate supply Application of potasshy

sium fertilizers to such plantings would undoubtedly improve

growth yields and reduce frost susceptibility

- 29 -

C Pineapple

1 Improved Cultural Practices

The easiest and cheapest way to significantly reduce frost

hazard to the pineapple plots visited would be to do a better

job of weed control and fertilization Better site location

particularly as regards downslope air drainage would also be

beneficial Pineapple like many crops is more sensitive

to frost when deficient in potassium supply Excessive nitroshy

gen applied in the fall can induce a tender flush of growth

which is more susceptible to frost damage but application of

a low-nitrogen high-potassium mixture has been found beneshy

ficial in several areas In Florida generous applications

of chopped tobacco stems were found to provide good nutrition

and increased frost tolerance

2 Covering with Thermal Insulators

Although pineapple can be damaged by exposure to --2 or -30 C

temperatures covering with palm leaves or other shading

greatly increases their frost tolerance In Florida covershy

ing with palmetto fans meadowgrass or lath-type shading

permitted tolerance of temperatures to -50 C Old banana

leaves or palm fronds should make good covering material for

pineapples in Paraguay

- 30 shy

3 Irrigation Water

Where available irrigation water could be used effectively

on pineapple for frost prevention Running water in furrows

between the rows would be the easiest procedure but overshy

head sprinkling would be even more effective providing a

dependable and continuous supply of pressurized water was

available

D Strawberries

The same general recommendations made for pineapple would apply

to strawberries because they are grown in a similar manner

Lightly covering with straw and running water between the rows

would be effective Overhead sprinkling would be very effective

but is subject to the hazards previously discussed (excess water

can be a problem equipment failure or stoppage during operation

can result in severe damage) Some selection for frost resisshy

tance might be effective as it has been in Michigan

VII Suggestions for Field Tests and Research Bearing on Frost

Protection

Application of techniques found effective elsewhere often need

to be modified to meet local needs and limitations Ideas which

look good on paper or in theory do not always live up to

- 31 shy

expectations in the field Before recommending procedures to

the many coops and their member farmers it would be prudent to

first test the proposed procedures under controlled conditions

A few demonstration plotq with cooperating growers or experishy

mental plots at the National Institute of Agronomy (IAN) could

be used to test or demonstrate the following

A Feasibility of interplanting Cavendish (short) and Mysore

(tall) bananas in colder locations to provide frost protecshy

tion by shading for the shorter more frost-sensitive Cavendish

B Tomato variety trial probably at IAN to look for new varieties

combining earliness high quality frost tolerance and resisshy

tance to Septoria and other prevalent diseases

C Influence of potassium supply on growth and frost resistance

of banana could best be tested and demonstrated on one or

more of the potassium-deficient plantings observed in the

field near Oviedo

D Effects of copper and antibiotic sprays on frost tolerance

could be determined by modifying current practices to provide

for frequent applications (2 to 10 day intervals) during

periods of high frost risk (mid-June to mid-August) This

vork should be conducted at the Institute until the benefits

if any as well as the details are worked out

- 32 -

E Procedures for combining shading materials such as palm

fronds with water in furrows under the vines could be worked

out under controlled conditions at IAN and then taken to the

field in the form of demonstration plots A simple procedure

is needed to provide thermal insulation on the south side of

tomato rows using plastic paper or dry vegetation to act as

a radiation shield on frosty nights

VIII Suggestions for Audio-Visual Aids

Since most of the participating farmers cannot read and many cannot

understand Spanish it would serve no good purpose to produce a

printed bulletin or Icaflet of the type used so effectively by the

Extension Service in the United States Instead since one picture

can often convey more information than many words a series of carshy

toon or comic book-like pamphlets or one-page answer sheets could

be produced for distribution through the participating coops If

the original drawings were made bulletin-board size (60 cm x 80 cm)

they could be reproduced as such for illustrated talks photographed

for slide shows and reduced to magazine size for the pamphlets or

answer sheets

Principles and concepts which could be put across in this manner

include the following

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones

- 29 -

C Pineapple

1 Improved Cultural Practices

The easiest and cheapest way to significantly reduce frost

hazard to the pineapple plots visited would be to do a better

job of weed control and fertilization Better site location

particularly as regards downslope air drainage would also be

beneficial Pineapple like many crops is more sensitive

to frost when deficient in potassium supply Excessive nitroshy

gen applied in the fall can induce a tender flush of growth

which is more susceptible to frost damage but application of

a low-nitrogen high-potassium mixture has been found beneshy

ficial in several areas In Florida generous applications

of chopped tobacco stems were found to provide good nutrition

and increased frost tolerance

2 Covering with Thermal Insulators

Although pineapple can be damaged by exposure to --2 or -30 C

temperatures covering with palm leaves or other shading

greatly increases their frost tolerance In Florida covershy

ing with palmetto fans meadowgrass or lath-type shading

permitted tolerance of temperatures to -50 C Old banana

leaves or palm fronds should make good covering material for

pineapples in Paraguay

- 30 shy

3 Irrigation Water

Where available irrigation water could be used effectively

on pineapple for frost prevention Running water in furrows

between the rows would be the easiest procedure but overshy

head sprinkling would be even more effective providing a

dependable and continuous supply of pressurized water was

available

D Strawberries

The same general recommendations made for pineapple would apply

to strawberries because they are grown in a similar manner

Lightly covering with straw and running water between the rows

would be effective Overhead sprinkling would be very effective

but is subject to the hazards previously discussed (excess water

can be a problem equipment failure or stoppage during operation

can result in severe damage) Some selection for frost resisshy

tance might be effective as it has been in Michigan

VII Suggestions for Field Tests and Research Bearing on Frost

Protection

Application of techniques found effective elsewhere often need

to be modified to meet local needs and limitations Ideas which

look good on paper or in theory do not always live up to

- 31 shy

expectations in the field Before recommending procedures to

the many coops and their member farmers it would be prudent to

first test the proposed procedures under controlled conditions

A few demonstration plotq with cooperating growers or experishy

mental plots at the National Institute of Agronomy (IAN) could

be used to test or demonstrate the following

A Feasibility of interplanting Cavendish (short) and Mysore

(tall) bananas in colder locations to provide frost protecshy

tion by shading for the shorter more frost-sensitive Cavendish

B Tomato variety trial probably at IAN to look for new varieties

combining earliness high quality frost tolerance and resisshy

tance to Septoria and other prevalent diseases

C Influence of potassium supply on growth and frost resistance

of banana could best be tested and demonstrated on one or

more of the potassium-deficient plantings observed in the

field near Oviedo

D Effects of copper and antibiotic sprays on frost tolerance

could be determined by modifying current practices to provide

for frequent applications (2 to 10 day intervals) during

periods of high frost risk (mid-June to mid-August) This

vork should be conducted at the Institute until the benefits

if any as well as the details are worked out

- 32 -

E Procedures for combining shading materials such as palm

fronds with water in furrows under the vines could be worked

out under controlled conditions at IAN and then taken to the

field in the form of demonstration plots A simple procedure

is needed to provide thermal insulation on the south side of

tomato rows using plastic paper or dry vegetation to act as

a radiation shield on frosty nights

VIII Suggestions for Audio-Visual Aids

Since most of the participating farmers cannot read and many cannot

understand Spanish it would serve no good purpose to produce a

printed bulletin or Icaflet of the type used so effectively by the

Extension Service in the United States Instead since one picture

can often convey more information than many words a series of carshy

toon or comic book-like pamphlets or one-page answer sheets could

be produced for distribution through the participating coops If

the original drawings were made bulletin-board size (60 cm x 80 cm)

they could be reproduced as such for illustrated talks photographed

for slide shows and reduced to magazine size for the pamphlets or

answer sheets

Principles and concepts which could be put across in this manner

include the following

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones

- 30 shy

3 Irrigation Water

Where available irrigation water could be used effectively

on pineapple for frost prevention Running water in furrows

between the rows would be the easiest procedure but overshy

head sprinkling would be even more effective providing a

dependable and continuous supply of pressurized water was

available

D Strawberries

The same general recommendations made for pineapple would apply

to strawberries because they are grown in a similar manner

Lightly covering with straw and running water between the rows

would be effective Overhead sprinkling would be very effective

but is subject to the hazards previously discussed (excess water

can be a problem equipment failure or stoppage during operation

can result in severe damage) Some selection for frost resisshy

tance might be effective as it has been in Michigan

VII Suggestions for Field Tests and Research Bearing on Frost

Protection

Application of techniques found effective elsewhere often need

to be modified to meet local needs and limitations Ideas which

look good on paper or in theory do not always live up to

- 31 shy

expectations in the field Before recommending procedures to

the many coops and their member farmers it would be prudent to

first test the proposed procedures under controlled conditions

A few demonstration plotq with cooperating growers or experishy

mental plots at the National Institute of Agronomy (IAN) could

be used to test or demonstrate the following

A Feasibility of interplanting Cavendish (short) and Mysore

(tall) bananas in colder locations to provide frost protecshy

tion by shading for the shorter more frost-sensitive Cavendish

B Tomato variety trial probably at IAN to look for new varieties

combining earliness high quality frost tolerance and resisshy

tance to Septoria and other prevalent diseases

C Influence of potassium supply on growth and frost resistance

of banana could best be tested and demonstrated on one or

more of the potassium-deficient plantings observed in the

field near Oviedo

D Effects of copper and antibiotic sprays on frost tolerance

could be determined by modifying current practices to provide

for frequent applications (2 to 10 day intervals) during

periods of high frost risk (mid-June to mid-August) This

vork should be conducted at the Institute until the benefits

if any as well as the details are worked out

- 32 -

E Procedures for combining shading materials such as palm

fronds with water in furrows under the vines could be worked

out under controlled conditions at IAN and then taken to the

field in the form of demonstration plots A simple procedure

is needed to provide thermal insulation on the south side of

tomato rows using plastic paper or dry vegetation to act as

a radiation shield on frosty nights

VIII Suggestions for Audio-Visual Aids

Since most of the participating farmers cannot read and many cannot

understand Spanish it would serve no good purpose to produce a

printed bulletin or Icaflet of the type used so effectively by the

Extension Service in the United States Instead since one picture

can often convey more information than many words a series of carshy

toon or comic book-like pamphlets or one-page answer sheets could

be produced for distribution through the participating coops If

the original drawings were made bulletin-board size (60 cm x 80 cm)

they could be reproduced as such for illustrated talks photographed

for slide shows and reduced to magazine size for the pamphlets or

answer sheets

Principles and concepts which could be put across in this manner

include the following

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones

- 31 shy

expectations in the field Before recommending procedures to

the many coops and their member farmers it would be prudent to

first test the proposed procedures under controlled conditions

A few demonstration plotq with cooperating growers or experishy

mental plots at the National Institute of Agronomy (IAN) could

be used to test or demonstrate the following

A Feasibility of interplanting Cavendish (short) and Mysore

(tall) bananas in colder locations to provide frost protecshy

tion by shading for the shorter more frost-sensitive Cavendish

B Tomato variety trial probably at IAN to look for new varieties

combining earliness high quality frost tolerance and resisshy

tance to Septoria and other prevalent diseases

C Influence of potassium supply on growth and frost resistance

of banana could best be tested and demonstrated on one or

more of the potassium-deficient plantings observed in the

field near Oviedo

D Effects of copper and antibiotic sprays on frost tolerance

could be determined by modifying current practices to provide

for frequent applications (2 to 10 day intervals) during

periods of high frost risk (mid-June to mid-August) This

vork should be conducted at the Institute until the benefits

if any as well as the details are worked out

- 32 -

E Procedures for combining shading materials such as palm

fronds with water in furrows under the vines could be worked

out under controlled conditions at IAN and then taken to the

field in the form of demonstration plots A simple procedure

is needed to provide thermal insulation on the south side of

tomato rows using plastic paper or dry vegetation to act as

a radiation shield on frosty nights

VIII Suggestions for Audio-Visual Aids

Since most of the participating farmers cannot read and many cannot

understand Spanish it would serve no good purpose to produce a

printed bulletin or Icaflet of the type used so effectively by the

Extension Service in the United States Instead since one picture

can often convey more information than many words a series of carshy

toon or comic book-like pamphlets or one-page answer sheets could

be produced for distribution through the participating coops If

the original drawings were made bulletin-board size (60 cm x 80 cm)

they could be reproduced as such for illustrated talks photographed

for slide shows and reduced to magazine size for the pamphlets or

answer sheets

Principles and concepts which could be put across in this manner

include the following

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones

- 32 -

E Procedures for combining shading materials such as palm

fronds with water in furrows under the vines could be worked

out under controlled conditions at IAN and then taken to the

field in the form of demonstration plots A simple procedure

is needed to provide thermal insulation on the south side of

tomato rows using plastic paper or dry vegetation to act as

a radiation shield on frosty nights

VIII Suggestions for Audio-Visual Aids

Since most of the participating farmers cannot read and many cannot

understand Spanish it would serve no good purpose to produce a

printed bulletin or Icaflet of the type used so effectively by the

Extension Service in the United States Instead since one picture

can often convey more information than many words a series of carshy

toon or comic book-like pamphlets or one-page answer sheets could

be produced for distribution through the participating coops If

the original drawings were made bulletin-board size (60 cm x 80 cm)

they could be reproduced as such for illustrated talks photographed

for slide shows and reduced to magazine size for the pamphlets or

answer sheets

Principles and concepts which could be put across in this manner

include the following

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones

- 33 -

A Frost - How it Forms and Where

1 Cold air drainage

2 Importance of slope

3 Importance of Elevation

4 Importance of Exposure

B Techniques for Preventing or Reducing Frost Hazard

1 Site Selection

2 Keep site and area above clean firm and moist

3 Cover plants with thermal insulation

4 Running water beside or under plants

5 Advantages and dangers of using overhead sprinkling for frost

control

6 When using fire many small fires are better than a few large

ones