Classification by selectivity and translocation mode
Understanding herbicide properties allows growers to select the appropriate active molecule for targeted weed challenges.
- Selective herbicides: Suppress target weed species without causing physiological injury to the cultivated crop.
- Non-selective herbicides: Destroy all green vegetation upon contact, used for pre-plant burndown or non-crop land clearance.
- Systemic (translocated) herbicides: Absorbed through foliage or roots and moved throughout plant vascular tissues to kill underground rhizomes.
- Contact herbicides: Destroy only the plant tissues directly wetted by the spray droplet, effective on young annual seedlings.
Application timing windows: Pre-plant, pre-emergence, and post-emergence
Applying herbicides during the appropriate physiological window determines both weed control efficacy and crop tolerance.
- Pre-plant incorporated (PPI): Applied into the seedbed before sowing to control emerging grass seeds and tubers.
- Pre-emergence: Sprayed after crop sowing but before the emergence of crops or weeds, requiring adequate soil moisture.
- Post-emergence: Applied to actively growing weeds during early vegetative stages (typically 2 to 4 weed leaf stage).
- Directed post-emergence: Sprayed between crop rows using hooded spray lances to prevent chemical contact with crop leaves.
Calibration, nozzle selection, and spray drift management
Proper spray equipment calibration prevents over-application and crop phytotoxicity. Operators should use flat fan or floodjet nozzles that produce medium to coarse droplets, avoid spraying during high wind speeds, and clean spray tanks thoroughly before switching to insecticidal or nutritional applications.
Official source
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ICAR Directorate of Weed Research ↗Related on KisanPe
Common questions
What is the difference between selective and non-selective herbicides?
Selective herbicides kill target weed species while sparing the crop; non-selective herbicides destroy all green plant tissue indiscriminately.
Why is soil moisture critical when applying pre-emergence herbicides?
Soil moisture is required to activate the chemical barrier in the topsoil so emerging weed seedlings absorb the lethal active ingredient.
Which spray nozzle type is best for applying agricultural herbicides?
Flat fan and floodjet nozzles are preferred because they produce uniform fan patterns with coarse droplets that minimise off-target wind drift.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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