Methods of Weed Control

Cultural Methods

• Timely sowing of cotton gives vigorous crop growth quick canopy coverage - suppress weeds.
• Band or pocket application of N-fertilizer to cotton reduces the nutrient availability for weed growth.
• Sowing certified seed.
• Adopt furrow method of irrigation.
• Raising cotton in paired rows and utilising the interspace effectively by cultivating intercrops like onion, greengram, bhendi etc., is found useful not only to reduce the incidence of weeds but also to obtain additional income per unit area.
• Proper crop rotation is highly useful for control of perennial weeds
• Mulching not only reduces weeds but also evaporation from soil.

• Deep ploughings, digging and removal of rhizomes or stolons or perennial weeds before sowing.
• Periodical harrowings reduces weeds and evaporation losses of moisture.

Chemical Control

Pre-planting

Soil incorporation of Fluchloralin (Basalin) at 2.0 ltr/ha as pre-sowing application upto 5cm deep is very useful to control mostly annual grasses and some broad leaved weed.

• Pre sowing application of Nitraline, Trifluralin, and Dinitramine at 1.0 kg/ha each. Alachlor 5.0 kg/ha or Diuron 1.5 kg/ha is very effective.
• For controlling Cyanodon, TCA at 5kg/ha as preplanting treatment is best.

Pre emergence application of Fluomaturon 3.0 kg/ha or diuron 1.2 kg/ha is most effective.

• Trifluralin 0.75 kg/ha and Nitralin 3kg/ha can control most grasses and sorghum halopense.
• Nitrofen 1.5 kg/ha as pre-emergence followed by MSMA at 5 lt/ha post-emergence can give good weed control. Monuron at 1.5 kg/ha may be used on excessively heavy soil.
• Chloropropham at 6 kg/ha can safely be used in both heavy and light soils as pre-emergence.

MSMA and DEMA at 2.0 kg/ha as post emergence application can control both annual and perennial weeds. However, TCA and Dalapon at 1% are well known herbicides to control perennial weeds like Cyanodon and sorghum Halopense (Johnson grass)

Weedicides used in Cotton

Selective

• Selectivity is the phenomena where in a chemical kills the target plant species in a mixed plant population without harming or only slightly affecting the other plants.
• It is considered to be the greatest single factor that helped in the success of chemical read control.

Non selective

• The chemical kills all parts what come in contact will the herbicide. They are also used as contact herbicides.

Translocated

• The plants absorb herbicides sprayed on plants and the toxic affects the growing parts and kills the plants.

Presowing

• Application of herbicide before the crop is sown or transplanted.

Pre-emergence

• Herbicide application after the crop is sown but before it has emerged.

Post-emergence

• Application of herbicide after the crop has emerged from the soil.

Details of Herbicides used in Cotton

Dalapon

Trade Name

• Dowpon

Formulations

• W.P = 85%

Selectivity

• A selective, translocated, pre and post emergence herbicide.

Weeds Controlled

• Effective control of perennial grasses such as sorghum halepense, cynodon doctylon, Agropyron repens
• control grasses like setaria sp., panicum sp., digitaria sp., annual and emergent water weed like typha sp.,

• Absorption and translocation is both by roots and shoots
• Uptake by leaves is significant
• Though the absorption continued for 48 hours but first six hours is most important.
• Translocated readily via both apoplastic and symplastic systems
• Main accumulation in growing tips and meristimatic tissue
• Inhibits elongation of roots within 4 hours and root growth ceased within 12 hours thus weakens regenerative capacity of grasses.
• Leaches rapidly in soils
• Persistance in soil is very fast only 2-4 weeks.
• High rate of application accute plant toxicity-Rapid precipitation of cell proteins-destruction of cell constituents-intensive scorching of leaves.

TCA (Trichloro acetic acid)

Formulations

• WP 90%

Selectivity

• Aliphatic compound.
• Selective translocated herbicide but at higher doses, it is non-selective and soil sterilant.
• Mostly applied to the soil as pre and post emergence and hence its uptake by roots is most significant.

• To control perennial grasses such as Johnson grass, (sorghum halopense) quack grass (Agropyron repens), Burmuda grass (cynodon dactylon) etc.,
• Also effective for aquatic weeds.

• Highly soluble and rapidly absorbed and translocated by roots. There after, it is exclusively transported via apoplastic system and accumulates in growing tissues.
• It reduces both cuticle and lamina thickness in leaves,
• Inhibits the enzymes, thus allowing the accumulation of toxic levels of free ammonia.
• Readily leached from the soil because of its high water solubility.

Dosage

• The normal dosage is 5 to 10 kg/ha. It is a strong acid. It is corrosive to iron, fine alluminium also, corrosive to skin and irritant to eyes and hence to be used cautiously.

Alachlor

Trade Name: Lasso

Formulations: EC 48%, Granules 10%

Selectivity:

• selective herbicide,
• mostly as pre-emergence spray on the soil and hence sufficient soil moisture is a pre-requisite for its effectivity.

• annual grasses and certain broad leaved weeds.

• Absorbs mainly near the first node of germinated shoots, secondarily by roots and translocated throughout the plant and then metabolized with in 10 days.
• Inhibits protein synthesis on susceptible plants.
• It inhibits growth of young seedlings by inhibiting root elongation, mitotic activity, enlargement of cells
• Inhibits production of by enzymes, amylase and protease in susceptible species.
• absorbed soil colloids, and the soil persistence is upto 10 weeks,
• no residual toxicity is found in the next crop because it breaks down with in 10-12 weeks.

Dosage

2-3 kg/ha.

Dinitramine

Trade Name: (Cobex)

Formulations: EC.25%

Selectivity

• selective pre emergence or pre planting herbicide which is sprayed in the field and incorporated after application.

• annual grasses and broad leaved weeds in cotton. The grassy weeds controlled include, ( barn yard grass, carpet weed, crabgrass, johnson grass, jungle rice, pursolane.)

• prevents germination of seeds and inhibits root growth.
• Strongly absorbed by soil and not leached through the soil.

Dosage

0.5 to 0.75 kg a/ha

Nitralin

Trade name: (Planavin)

Formulations: WP = 75%

Selectivity

• selective pre-emergence or pre-planting herbicide. Which is incorporated in the soil through mechanical means.

• Annual grasses and may broad leaf weeds particularly crab grass, water grass and foxtail are highly sensitive.

• not absorbed by plant foliage and there fore is not a post emergence herbicide.
• Absorbed only by seeds or roots by imbibing water.
• inhibits cell division.
• relatively immobile or stable in soil and leaches very slowly.

Dosage

0.5 to 2.0 kg/ha.

Trifluralin

Trade Name: Teflon

Formulation: EC 48% Granules 5%.

Selectivity

• a selective pre-emergence or pre-plant herbicide, applied on the soil and incorporated with in 8 hours after application.

• grasses like Echinochloa crusgalli, digitaria species, setaria spp., sorghum halopense and certain broad leaved weeds such as chenopodium album. Amaranthus spp., Tribulus terrestris, portulaca sp.,

• affects seed germination and only actively growing young tissues such as root tips and coleoptiles.
• It is not applied to plant foliage since there is no contact activity.
• several biochemical responses including changes in carbohydrates, lipids, nitrogen and nucleic acid content.
• inhibits nodule formation and induce nitrogen deficiency symptoms.
• inhibits accumulation of cotyledonory reserves.
• strongly absorbed on soil colloids and shows no leaching.
• persists in soil for 4 to 6 months and hence it has the potential for seasonal weed control.

Dosage

0.5 to 1.5 kg/hac.

Amitrole

Trade Name: weedazol, amizol.

Formulation: WP 50%

Selectivity

• heterocylic compound
• non-selective, translocated pre or post-emergence herbicide, mostly used in non-cropped areas.
• pre-plant treatment in cotton and orchards and also used as a defoliant in cotton.

• Perennial broad leaved weeds like Amaranthus viridis, Euphorbia sp., cirsium arvense (Canada thristle), Rhus radicams (poison ivy), Calotropis procera (milk weed); certain annual grasses/sedges Agropyron repens, cynodon dactylon, cyprus rotundus, poa annua, Allium sp., setaria gluca and also some aquatic weeds like Echornia crassipes, Typha sp., etc.,

• readily absorbed by the foliage.
• highly mobile and hence readily translocated to rhizomes of perennial weeds, deep in to the soil and injure auxillary buds. Through foliar application.
• Readily translocated to the meristimatic tissues through symplastic and apoplastic systems.
• inhibits chlorophyll formation, affects formation of chloroplasts in younger leaves, causing photosynthetic disruption and there by inhibits regrowth.
• Produces phytotoxic symptoms, showing bleaching first in young and then older leaves.
• is readily absorbed on organic soils but has very short residual life(2-4 weeks)

Diuron

Trade Name: Karmex.

Formulation: W.P 80%

Selectivity

• relatively non-selective herbicide and mostly applied as soil sterilant.
• at low rates, it acts as pre-emergence herbicide and selectively controls germinating broad leaved and grassy weeds.
• used as pre-emergence in cotton
• At high rates it acts as non-selective general weed killer and also act as soil sterilant in non-cropped areas.

• an effective weedicide for the control of annual and perennial grasses and herbacious weeds.
• the main weeds controlled are: Digitaria sp., Echinochloa crusgalli, Sorghum halopense, Setaria sp., and broad leaf weeds like Amaranthus sp., portulaca sp., Ipomea sp., chenopodium album etc.,

• absorbed mainly through the root system and translocated for leaves.
• inhibits photo synthesis and interferes with nitrogen metabolism.
• Used as pre-emergence treatment, provide adequate moisture in the soil to activate the herbicide.
• absorption is more in clay soil with organic matter content.

• 0.5 to 4 kg/ha in crop areas,
• 4-10 kg/ha for control of annual weeds 15 to 30 kg/ha for perennials in non cropped areas.

Monuron

Trade Name: Telvar

Formulation: WP 50%.

Selectivity

• an urea compound.
• non selective herbicide for general weed control in non-cropped areas. It is also used as selective pre-emergence herbicide in low doses (1-3 kg/ha) to control annual weeds.
• result is obtained when applied to just emerged weeds.

• grassy weeds controlled are Digitaria sp., Echinochloa crusgalli, Setaria sp., Sorghum halopense, and broad leaved weeds like Amaranthus, portulaca, chenopodium, convolvulus sp.,

• readily absorbed through root system and is translocated upward in the xylem.
• inhibits photosynthesis and interferes with nitrogen metabolism.
• At higher rates, phytotoxicity persists more than one season.

• at 0.5 to 5 kg/ha, but as a soil sterilant at 10 to 15 kg/ha against perennial weeds.