North Carolina

Flower Growers'

Bulletin Vol. 37, No. |October, 1992

^CIM-FLOM^

Official Publication of the North Carolina Commercial Flower Growers' Association

Low Volume Pesticide Application Systems

for the GreenhouseMichelle L. B. Crouse

Department of Entomology and Department of Horticultural Science

'hough high volume (HV) spraying isthe most traditional method of applying

pesticides in greenhouse and outdoor ornamentalsproduction, it isgenerallythoughttobeinefficientfor several reasons. There is a high variability ofdrop size withHV sprays. Duemainly to pesticidelabelling, wasteful dosages are often applied.For example, the phrase "spray to run-off orsimilar directions are given without regard tospray volume per crop area and means differentthings to different people. Most HV sprays areapplied manually, so distribution will vary withthe person making the application. Otherproblems include the time required to make theapplication, potential groundwatercontaminationfrom excessive run-off, and delayed re-entry intosprayed areas because of wet foliage. Despitethese problems, HV, "wet" sprays are consideredthe best general purpose method of applyingpesticides. Various equipment iswidely available,relatively inexpensive, and remains the only legalway to apply many pesticides. Also, HV spraysare adaptable to IPM programs because theyenable to grower to spot treat. Low volume

Tmethods, on the other hand, eliminate many ofthe disadvantages of conventional HVapplications: They take less time, use less wateror oil to dilute and carry the pesticide (norun off,faster re-entry), may use less pesticide, and theygeneratemostof thesprayvolumein small drops.

Spray drop sizeis important in determiningwhatkindofpesticide deposition anddistributionthere will be, no matter what the applicationmethod used. Often, the spray looks as if it'sdoing a great job of covering the target area,when, in fact, the spray drops are too large orsmall todeposit on the target. Most of the volumein HV sprays consist of large drops greater than100 to 400 microns in diameter (100 micronaverage diameter particles = 1mm). Low volumesprayers that produce a 10 micron averagediameterparticlewilldepositanaverageof 19,000particles or droplets in 1 cm2. HV applicationwould deposit only about 19 droplets in 1 cm2.Small drops can increase pesticide deposition. Anumber of studies have shown that with certain

insecticides, large numbers of small drops causehigher insect mortality than fewer, large drops.

N.C. Flower Growers'Bulletin Page2

Ready to use aerosols, sometimes calledtotalreleaseaerosols, can actuallybe consideredpre-packagedLVsprayers. Aerosolsareavailablefrom Whitrnire Research Labs, Inc. and othercompanies for management of whiteflies andother pests. A one pound can be used to treat3,000 square feet (of covered area) with spraydrops approximately 15 microns in diameter.Aerosol technology lends itself well to smallergreenhouses wherelarger LV equipment wouldbeimpractical. Unfortunately, no fungicides arecurrentlyavailableasaerosols. Activeingredientsrecently formulated as aerosols includebiphenthrin (Attain™ also known as the wettablepowder, Talstar™), fenoxycarb (Prelude™),acephate (Orthene™), pyrethrum,resmethrin,andmethiocarb. Whitrnire Research Labs is

developing a systemic aerosol from Miles nowreferred to as NTN.

Table 1 shows a comparison of the variouslow volume application equipment that isavailable. Highpressure hydraulic sprayers havea similar design to conventional hydraulicsprayers, but theyrequire amuch smaller volumeof water added to the chemical. The piston ordiaphragm pump forces the chemical solutionthroughthe nozzle ofahand-held spraygun. Thesolution exits the nozzle tip at high pressureandproduces an extremely fine spray with muchsmaller droplets than those created byconventional hydraulic sprayers working at 300to 600 psi. Applications are made by walkingthrough the areaaiming the spray produced by asingle nozzle ahead and down into the crop. ANC grower has noted that, though applicationtechnique is similar to that of HV, wet spraying,the applicator must walk much quicker becausethe stream is more concentrated. Results with

coldfoggers have been mixed. If the pest orpathogen is able to be contacted from above,control has been quite good. Coverage on leafundersides has been erratic, so pests such asspider mites and whitefly nymphs may not becontrolled effectively. Deposition on leafundersidesdependson planttype andhow easily

leaves can be moved in the spray stream. Veryflexible leaves are more likely to bend upward,exposing the leaf underside to the spray stream.

Electrostatic sprayers are similar to highpressure hydraulic sprayers but do not use a highpressure hydraulic pump. These machinesproduce a fine spray that is electricallychargedtoachievebettercoverage ofleafsurfacesandreducespraydrift. The negatively charged particles areattracted to any surface for providing coveragesimilar, theoretically, to high pressure hydraulicspraying with slightly better deposition on leafundersides. Air-assisted sprayers, havingcompressed airsupplied to the wand, air-blastthespray onto the crop and are more effective. Theonly air-assisted electrostatic sprayers now onthe market in the United States are produced byESS - Electrostatic Spraying Systems. Bothunattended (similar to mechanical aerosolgenerators) and hand-held, backpack models areavailable.

Problems include a "plant position" effect;in other words, deposition is greater and pestcontrol often better on plants nearest the spraynozzle. Studies have shown increased spraydeposition on plants using electrostatic sprays,comparedto other LV and HV sprays. However,most of this increase appears to be on uppersurfaces of leaves near the tops of plants. Thus,despiteadvancesinelectrostatic spraytechnology,distributionwithin the plantcanopy is stilluneven.This will vary with the pesticide, crop, sprayvolume,andperson makingtheapplication. Someof this variation can be reduced with properapplication techniques. Deposition on leafundersides can be increased and foliage canopypenetration improved by increasing the sprayvolume. At the higher spray volumes, the timerequired tomakean application maynotbemuchless than that for HV sprays over the same area.However, becausethe foliage isn' t wetted to runoff bythesprays, re-entry can bemaderight afterthe greenhouse is properly ventilated.

Thermal pulse-jet foggers use a pulsing jetengine to produce a highly visible fog that can

Table 1. Comparison of low volume spray a\opllcatlon equipmentf.

High pressure Air-assisted Thermal pulse-jet Rotary mistType: hydraulic electrostatic fogger applicator Mechanical aerosol generator

Dramm Motan Dramm Dramm

Example: Coldfogger™ ESS Back Pack Swingfog™ 50 Turbair Fox Autofog™ LVH Autofog™ SLVH

Spray drop average30 40 0.5-50 70-90 0.5-15 0.5-15

diameter (microns)

Operating pressure (psi) 2800-3000 40-50 4.4-5.9 18.5-28.5 14.2-22.8

Solution tank capacity 12 gal. 2.5 or 4 gal. 1.7 gal. 1 quart 3,7 gal. 1.85 gal.

Flow rate (gal./hour) 0-20 4 3.7-7.1* 1 0.87 0.71

Dispersal (galVacre) 14.5 max. 4-12 2.5-4.5** 0.5 2.5-6"* 0.5-1.1****

Time to treat 100,0001.5-2 2-9 0.5-1 1.5 several*** several****

square feet (hours)

Formulations that can liquids, wettable Liquids, wettable Liquids, wettable LiquidsLiquids, wettable Liquids, wettable

be applied powders powders powders powders powders

Price $3,200 $1,685 $1,700 $990 $5,000 $4,200

Advantages •Space sprayer, •Can be used in •Provides fastest •Can be used in •Space sprayer, operates unattendedoperates small houses and coverage for large small houses and •Deposition on undersides of leaves isunattended to spot treat (20 ft. areas (eg. gutter- to spot treat (6-15 above average

•Spray settles out of distance) connected range) ft. distance) •Most models have built-in tank agitatorsthe air rapidly; •Deposition on leaf •No need for carrier and automatic water rinse cycles forallows prompt undersides is if using water easy cleaningre-entry above average

•Small spray volumeand rapid dryingallows promptre-entry

nozzle

Disadvantages •Coverage on leaf •Can encounter a •Carrier solution •Few pesticides •Gummy residue (highly concentrated)undersides is "plant position may be required (eg. Rotospray can collect on all treated surfaces,

sometimes erratic effect" by manufacturer Resmethrin™)are including greenhouse structure•Coverage is •Can encounter a registered for use •Have set maximum coverage areas that

variable; human "plant position •Fan may blow cannot be exceeded without reducingapplicator effects effect" plants over at effectiveness (see *** and ****)can cause •Deposition on labelled applicationuneveness is undersides of distance

delivery leaves slightly less •Not available from

than average U.S. distributors

*Flow rate varies with nozzle used with the thermal pulse-jet fogger.**Rate of dispersal varies with nozzle used with the thermal pulse-jet fogger.***LVH model has a maximum coverage area of 70,000 square feet.****SLVH model has a maximum coverage area of 25,000 square feet.

N.C. FlowerGrowers'Bulletin Page 4

stay suspended in the air for up to six hours.Inside the fogger, a gasoline and air mixtureexplodes in the enclosed resonator, and theexplosion rushesout asajet stream. The chemicalsolution is injected into the jet stream and isblown apart into billionsof tiny particles. Thesevery small drops areable to move long distancesfromtheapplicator. With someofthelarger unitsavailable, drops can travel more than 200 feet.The size ofthe machine also determines the flow

rate of the liquid. Two-and-a-half gallons willcover about 50,000 square feet with a wettablepowder and 76,000 square feet with a liquidformulation. Specialized carrier solutionsproduce a visible fog, eliminate the evaporationof thechemical andensure uniformparticle size.Many manufacturers now provide special waternozzles that eliminate the need for carrier

solutions; using water solutions results in lessfogging action.

When using foggers to apply residualpesticides, especially wettable powderformulations, it is very importantto aimthe sprayabove the plantsatabouta30degreeangle. If thisisnotdone, heavydepositionin areas immediatelyin frontofthe foggerwill result,causingexcessivedosage and plantinjury. However, when appliedfrom above the crop, the pesticide distributionwithin the plant canopy and on leaf undersidesmay be poor. Thus, as with coldfoggers, usingthermal pulse-jet applicators with certainpesticide/pest combinations most likely will notbe successful. It may be feasible for growers whohaveexpandedmetal greenhouse benchesto makeapplications from below the crop, allowing thefog to rise up through the plant canopy. Thosewho have used this technique report good results.

Rotary mist applicators, originally calledcontrolled droplet applicators (CDA) or rotaryatomizers, are not widely available for use ingreenhouses in the United States. The type ofapplicator most widely-used worldwide ingreenhouses is the Turbair System. These areportable sprayers that disperse pesticides bydirectingthe flow ontorapidlyspinning,notched

discs. A fan behind the disc propels the spraytoward the target, creating a turbulent air stream.The time to treat a given area will vary with thecrop. Workers carry the sprayers through thecrop with awalking speed ofone pace per second.The spray is aimed ahead about 10 feet, directedat the plants, and moved up and down to ensureproper coverage. Obviously, bedding plants canbe treated more rapidly than cut roses, whichhave much more vertical growth requiring moreup and down passes. Pesticide deposition anddistribution is quite good. However, foliagecanopy penetration and leaf underside coveragevaries significantly, depending upon crop typesuch as roses, bench-grown potted plants orbedding plants on the floor. Most pesticidesapplied in rotary mist applicators are speciallyformulated for this use. Only one of thesepesticides, Rotospray Resmethrin™, is currentlyregistered for use with this equipment in theUnited States. Some growers have had successwith their own mixtures which they havecalibrated to ensure the correct dosage. Anypesticide registered for application as aconcentrate spray can be used in rotary mistapplicators.

Mechanical aerosol generators, sometimesreferred to as ultra-low volume (ULV) sprayers,use pressure supplied by an air compressor topump air through an air atomizing nozzle thatbreaks up the spray liquid into super-fine,fog-sized drops. Airisalsothemethodofmovingthe spray around the greenhouse and onto thefoliage. On most large models, a built-inconvection fan helps propel the spraydrops andcirculates air in the greenhouse to disperse thefog, and a timer allows machines to treat largegutter-connected ranges without an operatorpresent. Smaller models are also automatic, butdo not have a convection fan. With all of the

aerosol generators, much of the spraymovementisaccomplishedby the greenhouse airmovementsystem, i.e. horizontal air flow, overheadconvection tubes, and turbulator fans; run thesewhen aerosol generators are used.

Many growers find that integrating two ormore types of sprayers is the ideal. A popularcombination is a thermal fogger and a highpressureorconventional hydraulic sprayer. Thethermal fogger provides fast, broadcoverage andthe hydraulic sprayer affords easy spot treatment.The specific kind of low-volume sprayerchosenwill depend on many factors, includinggreenhouse size, whether the operationincludesmany separatehousesoronelarge,interconnectedrange,andthe crops produced. Forexample, youmay have a greenhouse where total releaseaerosols will be most practical. Others may haveavery large,opengreenhousethatrequires thermalfoggers or aerosol generators for best results.

N.C. Flower Growers' Bulletin Page 5

Low volume applicationshave the potentialto significantly reduce the amount of pesticideapplied while maintaining good pest control.The basic facts, however, are that technology iswell ahead of legality in many cases. Anyapplication method not prohibited on the labelcan be employed to apply a given pesticide.However, if a specific dilution (for example, 1poundper 100 gallons) isrequired, thiseffectivelyprevents low-volume applications, which mustbe made at very high concentrations (10 to 25times greater than HV sprays) to be effective.Most labels arewritten in this restrictive way, butchanges are occurring. Somepesticidecompaniesare modifying their product labels to allow forlow volume application.

NCCFGA NewsSam Franklin,

'he past year has been full ofchange forthe flower growers ofNorth Carolina.

Our industry continues to grow by leaps andbounds in production of certain crops. As wegrow, our organization needs have grown. Ourincreased visibility and the need to be more proactive necessitate that we formulate a plan thatwill allow our organization to become moreresponsive to the needs of the membership.

The North Carolina Commercial Flower

Growers' Association voted in its annual meetingOctober 12,1992 to hire Betty Woodhouse as anexecutive director. The establishment of a

permanent office with a phone will help theAssociation be more effective in its mission to

promote the floral industry and increase theprofitability of our profession.

This kind of change does not come withoutcosts. Your BoardofDirectorsdid notrecommend

this change without formulating a plan of action

Past-President

thatwas fiscallyresponsible. To my knowledgewe have never formally adopted a budget untilthis year. The Association adopted the budgetfound in this issue. The budget also representschange. We adopted a new dues structure. Wehave actually lowered the dues for some of oursmaller greenhouse firms. The majority of themembershipwill only see a$10 increasein dues.

Looking at the numbers, it is fascinating tosee that over half of our membership is 1 acre orless in size. Please take the time to make yourneighbors aware of these changes. With yourhelpwecanmakethe 10%increasein membershipthat is required to meet this budget Increasednumbers mean betterdissemination ofknowledgethat will make us all more profitable, give usmore political clout, make us a better and moreresponsive organization.

Finally, thank you for allowing me to servethis past year as president.

<? \The 1992 NCCFGAMembership Directory/Short Course Show Bookwasgiven out during the Short Course earlier this month. Call Doug Baileyat

(919) 515-3321 if you would like to receive a copy.