Classification of agricultural herbicides
- Selective herbicides: Target specific weed types without causing injury to the established crop (e.g., 2,4-D in wheat, Atrazine in maize, Pretilachlor in rice).
- Non-selective herbicides: Eradicate all green vegetation upon contact (e.g., Paraquat, Glyphosate), used in fallow fields, bunds, or non-crop areas.
- Pre-emergence herbicides: Applied to the soil surface before weed seeds germinate, creating a chemical barrier that stops emerging sprouts (e.g., Pendimethalin).
- Post-emergence herbicides: Applied directly onto growing weed foliage after crops and weeds have emerged (e.g., Bispyribac-sodium, Halosulfuron).
Contact versus systemic modes of action
- Contact herbicides: Destroy only the plant tissues directly touched by the chemical droplet (e.g., Paraquat), requiring complete spray coverage.
- Systemic herbicides: Absorbed by foliage or roots and translocated throughout the plant's vascular system to kill underground rhizomes and roots (e.g., Glyphosate, Metsulfuron).
- Application technology: Use flat-fan or floodjet nozzles delivering coarse droplets to prevent off-target wind drift onto sensitive adjacent crops.
Safe application, tank calibration and environmental protection
Accurately calculate dosage per acre based on product label instructions and never use domestic containers for chemical mixing. Dedicate specific sprayers for herbicides, or wash tanks thoroughly with water and detergent before spraying insecticides or fungicides, as herbicide residues can severely damage subsequent crops. Always wear protective rubber gloves, masks, and boots.
Official source
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Central Insecticides Board & Registration Committee (CIB&RC) ↗Related on KisanPe
Common questions
What is the difference between selective and non-selective herbicides?
Selective herbicides kill specific weeds while leaving the crop unharmed, whereas non-selective herbicides kill all green vegetation they contact.
When should pre-emergence herbicides be applied?
Pre-emergence herbicides are applied to moist soil after sowing but before crop and weed seeds germinate, typically within 24 to 72 hours of planting.
Can the same sprayer be used for herbicides and insecticides?
It is best to keep a separate sprayer for herbicides; if using the same equipment, wash the tank, pump, and nozzles thoroughly with detergent to avoid damaging crops with residual herbicide.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
More Crop Protection & Pesticides guides
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