Agricultural Weedicides: Types, Application Timing and Safety

Classification by selectivity and action

• Selective weedicides: Eliminate target weed species while leaving the main crop undamaged (e.g. 2,4-D in wheat or sugarcane, and Imazethapyr in soybean and pulses).
• Non-selective weedicides: Destroy all green plant tissue upon contact (e.g. Glyphosate and Glufosinate-ammonium), used for clearing uncropped bunds, channels, and zero-tillage seedbeds.
• Systemic vs contact: Systemic weedicides translocate to kill weed root networks; contact weedicides destroy only the foliage directly wetted by the spray.

Application timing: Pre-emergence versus post-emergence

Pre-emergence weedicides are sprayed on moist soil after crop sowing but before weeds germinate, forming a chemical barrier in the top 2 to 3 cm of soil. Post-emergence weedicides are applied directly onto young, actively growing weeds when they are at the 2 to 4-leaf stage and the crop canopy is established.

Nozzle selection, calibration and sprayer hygiene

• Always use flat-fan or flood-jet nozzles operating at low pressure (15 to 20 psi) to generate coarse, uniform droplets that resist wind drift.
• Never use hollow-cone nozzles for weedicides as fine mist drifts onto companion crops and causes severe chemical burning.
• Triple-rinse spray tanks and hoses with fresh water and detergent immediately after spraying before using the pump for other inputs.

Related on KisanPe

• Crop protection guide →
• Pesticide calculator →
• Wheat farming guide →
• Ask Sakhi AI →

Common questions

General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.