Presented by

Nishanth S

Weed

Jethro Tull first coined the term ‘weed’ in 1931 in the book “Horse Hoeing

Husbandry”

DEFINITION:

• “Weeds are unwanted and undesirable plant that interfere with utilization of land

and water resources and thus adversely affect crop production and human

welfare.”

• “Weeds are the plants, which grow where they are not wanted.”

(Jethro Tull, 1731)

Characteristics of weed

CHARACTERISTICS:

1) In the world 30,000 species of weeds have been listed.

2) Out of which 18,000 cause serious damage to agricultural production.

3) 18 weeds are considered as world worst weeds.

4) These weeds are more competitive than the cultivated crops.

5) They are capable of thriving under stress condition. They produce enormous

seeds.

6) The weed seeds are easily germinated, they undergo pollination very easily.

Harmful effects of weeds

Harmful effects of weeds:

• Compete with crop – space, light, moisture, nutrients: YIELD REDUCTION

• Affects quality – farm produce, livestock products such as milk and skin.

• Acts as alternate host – pests and pathogens.

• Causes health problems. Eg., Parthenium causes allergy.

• Increases cost of cultivation – weeding problem.

• Reduces the land value.

• Some weeds are poisonous to livestock.

Beneficial effects of weeds

Beneficial effects of weeds:

• As a manure – eg., Calotropis gigantea, Croton sparsiflorus, Tephrosia purpuria

• As human feed – eg., Amaranthus viridis, Digera arvensis as greens

• As fodder – eg., Rynchosia aurea, R. capitata, Clitoria terne (legume fodder)

• As fuel – Prosopis julilora, make charcoal and marketed.

• As soil binder – eg., Panicum repens

Beneficial effects of weeds

• As medicine:

• As mats and screens - eg., Cyperus pangorei & C. corymbosus: making mat

Typus angustata: making screen

• As indicators for good and bad soil –

Phyllanthus niruri Jaundice

Eclipta alba Scorpion string

Centella asiatica Improves memory

Cynodon dactylon Asthma, Piles

Cyperus rotundus Stimulated milk secretion

E. colonum Rich soil

Cymbopogon Poor light soil

Sedges Ill-drained soil

Classification of weeds

WEED

Life span Ecological

affinity

Soil type Origin Morphology

Annuals

Biennials

Perennials

Wetland

Garden land

Dry land

Black cotton soil

Red soil

Light, sandy or

loamy soil

Lateritic soil

Indigenous

Introduced or

exotic

Grasses

Sedges

Broad leaved

Note : Cyperaceae and typhaceae are not grasses even though they are narrow leaved

Yield losses caused by weeds in some plants

• Management of weeds is an important component of production technique as

eliminating of weeds is expensive and hard to achieve.

• The basic approach – to minimize production cost caused by weeds, though

weeds may exist as a part of the whole ecosystem.

CROPYIELD REDUCTION

(%)CROP

YIELD REDUCTION (%)

Rice (transplanted) 30-40 Wheat 20-30

Rice (drilled) 70-80 Soybean 40-60

Maize 50-70 Groundnut 40-50

Sorghum 50-70 Mustard 10-15

Pulses (Kharif) 40-60 Cotton 40-50

Pulses (Rabi) 20-30 Sugarcane 20-30

Potato 30-60

‘Minimum loss in crop production and least disturbance to the ecosystem’

About Organic weed management

Weed management

• DEFINITION:

“Weed management is the application of certain principles and suitable

methods that will improve the vigour and uniform stand of the crop. At the same

time ignore or discourage the invasion and growth of weeds.”

Evolution of weed management: (6 stages)

1. 10,000 BC Removed by hand

2. 6000 BC Weeds removed by primitive hand tools

3. 1000 BC Weeding done with the help of animal drawn implements

4. 1920 AD Machine drawn implements were used for weeding

5. 1930 AD Weeding was taken up by biological agents

6. 1947 AD Weeding by chemical methods (organic herbicides)

Principles of weed management

• Prevention

• Eradication

• Control

• Management

PREVENTION:

1. Use of clean seeds.

2. Avoid the use of raw dung as manure.

3. Avoid movement of livestock and implements from weed infested area to the

clean area.

4. Keep farm fences, roads and bunds clean or free from weeds.

5. Avoid soil transport from weed infested area.

6. Keeping irrigation channels and canal bunds clean.

7. Pull out seedlings in nurseries carefully without weed seedlings.

Curative methods

CURATIVE METHODS: control of weeds in the field

A. Eradication methods:

Weeds are destroyed immediately before its multiplication, dispersion and

acclimatization as and when a new weed species is found. It can be done by-

• Destroying the species at the initial stage of introduction and before it produces

any propagule.

• Degenerating the buried dormant viable seeds by fumigation, flooding, heating

and other methods.

B. Control measures:

• In these method weeds are not eradicated but their growth is checked and the

number of weeds is minimized so that they do not affect crop yield.

Methods of weed control

METHODS OF WEED CONTROL:

• Mechanical or Physical method

• Cultural mthod

• Chemical method

• Biological method

Mechanical method

Hand weeding

Removal of weeds either manually or by using tools like khurpi or sickle, when

weeds grown upto some extent.

Effective against annuals and biennials and controls only upper portion of the

perennial.

Higher labour is required and is tire some.

1. Hand weeding 7. Flooding

2. Hand hoeing 8. Burning

3. Spudding 9. Soil Solarisation

4. Digging 10. Cheeling

5. Sickling 11. Tillage

6. Dredging and chaining 12. Mulching

Mechanical method

Hand hoeing

• Hoe has been the most appropriate and widely used weeding tool for centuries.

• Taking out the weeds with the help of khurpi or hand hoes.

• Hoeing by cutting the crown part gives proper control.

• Annuals and biennials can be effectively controlled.

• Convolvulus arvensis which has shallow root system can be controlled.

Mechanical method

Spudding

• Hand weeding, hand hoeing added by a sharp edged sickle.

Sickling

• Sickling is also done by hand with the help of sickle to remove the top growth of weeds to prevent seed production and to starve the underground parts.

• These methods are useful for control of tall growing grasses.

• Especially sickling is useful in irrigation channels, drainage channels and where undulating topography is present.

Mechanical method

Digging

• Digging is useful for patch or spot control of obnoxious / perennial weeds.

• Digging is very useful in the case of perennial weeds to remove the underground propagating parts of weeds from the deeper layer of the soil.

• They can be eliminated by digging with crowbar or Pick axe etc.

• For large areas, it is not desirable because it is costly and labour oriented.

Mowing

• It is cutting of uniform growth from the entire area up to the ground level.

• It is useful more in non cropped areas than cropped areas. Mowing improves aesthetic value of an area. Effective against erect and herbaceous weeds.

Mechanical method

Cutting

• Cutting is the topping/cutting of the weeds little above ground level.

• It is done with help of axes and saws.

• It is mostly practiced against brushes and trees. In aquatics under water weed cutters are used.

Dredging

• This is used to control aquatic weeds growing in shallow ditches.

• Mechanical pulling of aquatic weeds along with their roots & rhizomes from the mud.

Mechanical method

Chaining

• Very big & heavy chain is pulled over the bottom of a ditch with tractors along

with embankments of ditch.

• With rubbing action of chain weeds can be fragmented & collected by nets and

hooks.

Burning

• It is cheapest method to eliminate the mature unwanted vegetation in non-cropped

areas and range lands.

• Coagulation of protoplasm occurs with which plant dies.

Mechanical method

Flaming

• It is the momentary exposure of green weeds to as high as 1000oC from flame

throwers to control in row weeds.

• Eg. Flaming is used in western countries for selective weed control in crops like

cotton, onion, soybean and fruit orchards. Dodder is also controlled by flaming

in lucern.

Searing

Repeated application of flame to above

ground parts destroyed the root system

and plant dies

Mechanical method

Soil Solarization

• It is also called solar soil heating.

• It is effective against weeds which are

produced from seeds.

• It doesn’t involve any tillage of the

field.

• Covering the soil with transparent,

very thin plastic sheets of 20-25mm

polyethylene (PE) film during hottest

part of summer months for 2-4 weeks.

• This increases the temperature by 10-12 0 C over the unfilmed control fields. Then

weeds seeds are desiccated which are present at top 5 cm soil depth.

• Eg: Philaris minor, Avenae and broad leaved weeds controlled by Solarization.

Where as Melilotus sp. posses hard seed coat is resistant to Solarization treatment.

Mechanical method

Cheeling

• An implement called cheel (spade

like implement with very long handle)

with which weeds & soil can be

racked up.

• Generally practiced in tea plantations.

Tillage

Most effective and economic method of weed control.

Ploughing, cultivating and harrowing make possible weed control before sowing.

Mould board plough – controls perennial weeds.

Disc harrow and chisel plough Primary tillage operation

Discs, cultivators and harrows Seed bed preparations

Cultivators, discs, rod weeders,

harrow and rotary hoes

Post-seeding weed control

Mechanical method

Table: Influence of primary tillage on total weed seeds in soil

Role of tillage in weed control:

a) Facilitating the germination of weed seeds, which can, then, be easily destroyed

by mechanical means.

b) Bringing roots or stolons to the soil surface where they will dry out under the

sunlight.

c) Repeated cultivation, thereby depleting the food reserve of the plant.

d) Uprooting or smothering the weeds with soil.

Soil depth (cm) Total weed seed (%)

Ploughed Chiseled

0-5 20 63

5-10 27 20

10-15 53 17

Mechanical method

Puddling:

Primary objective- to create impervious soil layer to prevent percolation.

Secondary objective- to destroy weed seeds and weed seed gets decayed.

Mechanical method

Intercultivation:

Most effective in the crops sown in rows especially with hoes.

Treatment Weed population (No./m2)

Weed control efficiency (%)

Seed yield (kg/ha)

Unweeded control 216.93 - 783.19

One hoeing (25 DAS) 100.45 39.72 897.38

Two hoeing (25 & 50 DAS) 18.85 92.32 245.72

Table: Effect of hoeing on weed population, weed control efficiency and yield of greengram

(Panwar etal., 1999)

Mechanical method

Mulching

• Principle is exclusion of sunlight from

environment.

• Polythene Sheets, natural materials

like paddy husk, ground nut shells,

saw dust etc. are used as mulching

material.

• The thickness should be enough to cut

off light (i.e. 10-15 cm)

• The efficiency of polythene sheet is more (more polythene) if it is applied in

continuous sheet rather than in particle farm.

• It is effective against annual weeds and perennial weeds like Cynodon dactylon

and Sorghum halapense.

Mulch

levels

No. of weeds /m2 Weed dry weight (g/m2)

1985-86 1986-87 1985-86 1986-87

No mulch 31.8 16.9 17.4 12.7

Trash mulch 25.9 14.0 15.2 12.1

Table: Effect of mulching on weed growth

(Mann and Chakor, 1993)

Table: Effect of wheat straw mulch on weed growth in maize

Mulch level (t/ha) Weed population (kg/ha)

Weed dry weight (kg/ha)

0 220 1500

1.7 160 1800

3.4 67 950

5.1 57 680

6.8 53 570

(Crutchfield, 1986)

Mechanical method

Cultural methods

Proper crop stand and early seedling vigour

• Lack of adequate plant population is prone to heavy weed infestation, which becomes, difficult to control later. Therefore practices like

are very important to obtain proper and uniform crop stand capable of offering competition to the weeds.

1. Proper crop stand and early seedling

vigor

7. Smother crops

2. Selective crop simulation 8. Minimum tillage

3. Proper planting method 9. Summer fallowing

4. Planting time 10. Lowering area under bunds

5. Crop rotation 11. Flooding and drainage

6. Stale Seedbed

a. Use of high viable seeds c. Adequate seed rate

b. Selection of most adopted crops and crop

varieties

Cultural methods

Planting density:

In the crop-weed competitive suituation, by means of narrow spacing or

high seed rate higher number of plants gain bolder canopy cover and thereby

higher weed suppression capacity.

Spacing (cm)Weed weight

(g/0.25m2) Grain yield (kg/ha)

20 x 2.5 8.81 4100

20 x 5.0 20.33 3700

20 x 10.0 13.87 3000

20 x 15.0 23.09 3200

20 x 20.0 26.16 3900

Table: Effect of spacing on weed growth in transplanted paddy

(Kim and Moody, 1981)

Dec

reas

e in

sp

acin

g Increase in

yield

Cultural methods

Planting direction:

• Crops sown in North-South direction suppress weed growth better than East-West

direction.

• East-West crop allows sunlight to reach weeds throughout the day whereas,,

North-South sown crop utilizes more light, shades weeds and does not allow light

to reach weeds.

Seed rate (kg/ha) Grain yield

(kg/ha)

Dry matter of

weeds (kg/ha)

100 3477 831

125 3549 457

150 3688 280

Table: Effect of seed rate on weed dry matter and yield of wheat

(Bhan, 1987)

Cultural methods

Selective crop simulation:

• Selective simulation can be achieved by

a) application of soil amendments like gypsum or lime may correct the soil

conditions in favour of crop growth

b) addition of FYM or synthetic soil conditioners to very light or heavy soils

may improve the soil structure and maintaining better air water relationships and

ultimately it improving the crop growth

c) manures and fertilizers application of proper kind in adequate quantities

improve the crop growth.

d) Inoculation of crop seeds with suitable nitrogen fixing and phosphorous

solubilising organisms may helps in selective simulation of some crops.

Eg: Legume crop and non legume weed. Selective simulation in wide row crops like

maize, sugarcane, cotton can be achieved by foliar application of nutrients.

Cultural methods

Proper planting method

• Any planting method that leaves the soil surface rough and dry will discourage

early growth.

• Plough planting (minimum tillage) methods proved to be very useful to reduce

early weed growth.

• In summer, furrow planting of crops reduce the weed problems. Because in this

method irrigation water restricted initially to the furrow only.

Cultural methods

Irrigation methods:

• The weed growth is higher and more pronounced in surface method of irrigation

than drip.

• In Rice, one day after disappearance is always better than continuous

submergence in checking weed growth and improving yield.

• It is more suitable in SRI method of rice planting.

DAT of Cabbage No. of weeds Dry wt. of weeds

Drip Furrow Drip Furrow

30 1409 1844 128 157

60 948 1530 129 170

80 352 1165 44 61

Table: Effect of drip and furrow irrigation on weed intensity in cabbage

(Kudmimani, 1997)

Cultural methods

Planting time

• Peak period of germination of seasonal weeds coincides with crop plants.

• So little earlier or later than normal time of sowing is beneficial by reducing early

crop weed competition.

• Eg: Using photo insensitive varieties we can make adjustments with regarding to

time of planting.

Treatment Grain yield (kg/ha) Dry matter of weeds @

95DAS (kg/ha)

12 November 4148 1662

24 November 3670 1493

5 December 3637 1124

17 December 2890 9551

Table: Effect of date of sowing on weed dry matter and grain yield of wheat

(Bhan, 1987)

Cultural methods

Crop rotation

• Growing of different crops in recurrent succession on the same land is called as

crop rotation.

• Monocropping favors persistence and association of some weeds.

• Crop rotation is effective in controlling of crop associated and crop bound

weeds such as Avena fatua in wheat.

• Wheat-pea and gram break the Avena in wheat, Lucern - grain crop rotation

control Cuscuta.

• The obnoxious weeds like Cyperus rotundus can be controlled effectively by

including low land rice in crop rotation.

Principles in crop rotation:

• Rotation of competitive crops and non-competitive crops.

• Use of weed suppressing crops as cover crops.

• Under sowing cereals with fodder legumes.

• Use of catch crop or trap crop.

Cultural methods

Stale Seedbed

• It is the one where one or two flushes of weeds are destroyed before planting of

any crop.

• This is achieved by soaking a well prepared field with either irrigation or rain and

allowing the weeds to germinate.

• These weeds are controlled by using mechanical methods then sow the crop. Here

the advantage is the crop is germinated in weed free environment. In this way,

weed seed bank is exhausted.

Smother crop / Competitive crop

• This crop germinates very quickly and develop large canopy, capable of efficient

photosynthesis within short period.

• They possess both surface and deep roots. Competitive crop smother the ground

quickly than non competitive crop.

• Eg; Cowpea, lucern, berseem, millets.

Cultural methods

Growing of intercrops

• Inter cropping suppresses weeds better than sole cropping and thus provides an

opportunity to utilize crops themselves as tools of weed management.

• Many short duration pulses viz., green gram and soybean effectively smother

weeds without causing reduction in the yield of main crop.

Cultural methods

Minimum tillage

• Deep and frequent tillage may be useful for some reasons but it serves to bring

more of dominant weed seeds and rhizomes to the soil surface .

• Preserve the new weed seeds deep in the soil for the future Zero tillage

completely avoids burying of weed seeds and reduces persistence of annual

weeds but it induces vigorous growth of perennial weeds.

Treatment Sorghum yield (kg/ha) Weed dry weight (g/m2)

Sorghum + 1 HW 3652 78.7

Sorghum + 2 HW 5264 17.0

Sorghum + Cowpea 1 HW 4895 8.3

Sorghum + Greengram

1HW

3952 14.7

Table: Effect of intercropping on grain yield of sorghum and weed weight at harvest

(Rao and Shetty, 1981)

Cultural methods

Summer fallowing

• The practice of summer tillage or off-season tillage is one of the effective

cultural methods to check the growth of perennial weed population in crop

cultivation.

• In the month of April, May and June farmers expose their lands to sun in order to

control many soil born pests, including weeds, roots, rhizomes and tubers of

shallow rooted perennials like Bermuda grass and nut sedge.

Cultural methods

Lowering area under bunds

• Bunds are made in field for the purpose of irrigation is ideal places for the rapid

growth of weeds.

• One way of tackle the problem of weeds on bunds is to level the land well so that

less no. of bunds is needed to irrigate the field.

Flooding and drainage

• Flooding is world wide crop husbandry method controlling weeds in rice fields.

• Controls terrestrial weeds: To ensure the effectiveness of flooding the weeds

should be submerged sufficiently for a longer period (i.e. for 2 weeks or more).

Excludes O 2 from environment and kills the weed.

• In M.P. deep flooding of fallow land is followed in rainy season and water is let

out after 2-3 months. This practice locally called Haveli.

• Drainage is used for controlling aquatic and semi aquatic weeds in rice fields,

channels, canals, and ponds.

Biological methods

It involves the deliberate use of living organisms like insects, fish, disease

causing organisms or competitive plants to limit weed infestation.

Bioagent:

Ideal characteristics—

Host specificity

Ability to kill weed or prevent its reproduction

Good adaptability

Reproductive capacity at a rate sufficient to maintain control of host

High ability to disperse successfully and to locate its host plant.

Strategies

Classical approach Bioherbicide

approach

Naturally occuring

herbicides

Classical approach

• Steps involved:

Selection of suitable target

weed species

Selection of suitable bio-

control agents

Introduction, liberation and

establishment of control agents

Selection of survey areas for bio-control agents

Selection of effective bio-control agents

Host specificity determination

1

2

3

Classical approach

TYPES OF CLASSICAL BIO-AGENTS

Specific Non - Specific

attack only one or two

specific weeds

Feed upon a variety of

vegetation

Insects

Plant pathogen

Competitive

plants

Carp fish

Snail

Mites

SPECIFIC BIO-AGENTS

Insects

Crocidosema lantana (moth) Lantana camara

Plant pathogens

Cephalosporium zonatum Acacia glauca

Puccinia chondrillana Skeleton weed (Chondrilla juncia)

Competitive plants

Marigold & Cassia sericea Parthenium

Panicum purpurascens Typha sp

Carp fish- SPECIFIC

Ctenopharyngodon idella (Chinese grass

carp) Aquatic weeds

Cyprinus carpio (common carp)

Marisa cornuarietis (Snails) roots of water hyacinth, water lettuce and

leaves of “Salvinia”.

Tetranychus desertorum (Mite) prickly pear “Opuntia dellini”

Examples of Bio-agents

Bioherbicides / Mycoherbicides

“Bioherbicides are pathogens cultured artificially and made available in sprayable formulations; just like a chemical herbicide.”

Pathogen Weed controlled

Collectotrichum furarioides Asclepias seriaea Common milk weed

Alternaria sp. Crisium avense Canana thistile

Phomomsis convolvulus Convolvulus arvensis Field bind weed

Alternaria crassa Datura stramonium

Bipolaris halepense Sorghum halepense Johnson grass

Collectotrichum oriculare Xanthium spinosum Spiny cocklebur

Alternaria helianthi X. stramarium

Table: Fungi possessing mycoherbicidal activity

Bioherbicides / Mycoherbicides

Table: Commercial Mycoherbicides

The rust pathogen, Puccinia abrupta var. parthinicola is capable of

controlling Parthenium hysterophorus.

(Recent report)

Characteristics of good mycoherbicides

• They should be

1. Culturable in artificial media

2. Capable of abundant spore production

3. Stable in storage

4. Genetically stable

5. Effective under field conditions

6. Tolerant to variations in temperature

7. Compatible with other chemical/cultural practices

Constraints in bioherbicide approach:

1. Pathogen virulence

2. Environmental reuirements

3. It remains active only on the current weed population

Allelopathy in bio-control programmes

1. Use of cover crops for bio-control:

Parthenium incorporated into soil

reduces growth of Cynodon dactylon.

Leachets of dry plants of cumin

control weeds.

Velvet bean suppresses purple nut

sedge.

2. Use of allelochemicals as natural herbicides:

Xanthotoxin inhibits germination and growth of Lactuca sativa.

AAL toxin (Alternaria alternate lycopersicii) – effective against dicots at low

concentration.

• The living plant as well as the crop residues with allelopathic potential releases

allelochemicals and suppresses weed growth.

Allelopathic potential of some crops

Plant species and common name Inhibition (%)

Medicago sativa (Alfalfa) (cv. Rasen): leaves & stem 100.0

Medicago sativa (Alfalfa) (cv. Yuba) : leaves & stem 100.0

Piper methysticum (Kava): root 100.0

Medicago sativa (Alfalfa) : pellets 85.0

Azadirachia indica Juss neem: leaves & bark 81.3

Leucaena glauca (White lead-tree) 80.7

Ageratum conyzoides (Billy goat weed) 67.0

Galactia pendula (Galactia) 65.4

Eupatorium canabium (Fragrant throughoutwort) 64.9

Oryza sativa (Rice) (cv. Koshihikari): bran 60.7

Melia azedarach (China berry) 58.1

Blechnum orientale (White fern) 52.8

References

Websites:

• www.agritechportal.in

• www.angrau.in

Text Books:

• S. C. Panda, Principles and Practices of Organic Farming, pg no. 477- 489

• R. Balasubramanian, K. Balakrishnan, K. Sivasubramaniam, Principles and

Practices of Organic Farming, pg no. 209-219

• S. P. Palaniappan, K. Annadurai, Organic Farming Theory and Practices, pg no.

112-130