Classification by selectivity and mobility
Understanding herbicide types is vital for selecting the correct product without harming cultivated crops.
Primary classifications include:
- Selective herbicides: Formulations engineered to suppress specific weed species while leaving the primary crop undamaged (for example, Pendimethalin in soybean or Atrazine in maize).
- Non-selective herbicides: Broad-spectrum chemicals that destroy all vegetation they contact (such as Glyphosate or Glufosinate Ammonium), used in non-crop areas or pre-sowing.
- Contact herbicides: Chemicals that kill only the plant tissue they directly touch without internal translocation (such as Paraquat Dichloride).
- Systemic herbicides: Compounds that are absorbed by leaves or roots and translocate throughout the vascular system, eliminating deep subterranean weed rhizomes and tubers.
Application timing: PPI, Pre-emergence and Post-emergence
Herbicides are applied at precise agronomic stages to achieve optimal weed control:
Application timing stages:
- Pre-Plant Incorporated (PPI): Mixed mechanically into the topsoil prior to seed sowing to control emerging weed seeds.
- Pre-emergence (PRE): Applied uniformly to moist soil surface after crop sowing but before crop seedlings and weed seeds emerge.
- Post-emergence (POST): Sprayed directly over standing weeds after both the crop and weeds have emerged from the soil.
- Directed post-emergence: Sprayed between crop rows using hooded nozzles to prevent chemical contact with the crop canopy.
Safe application practices and resistance management
Proper calibration of spray nozzles (such as flat-fan or flood-jet nozzles), maintaining adequate soil moisture, and following registered label dosages are crucial for effective herbicide performance. Continuous use of a single herbicide mode of action can lead to resistant weed biotypes; farmers should implement integrated weed management (IWM) including crop rotation, manual hoeing, and chemical rotation.
Official source
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ICAR - Directorate of Weed Research (DWR) ↗Related on KisanPe
Common questions
What is the definition of a herbicide?
A herbicide is an agricultural chemical or biological formulation specifically designed to control, suppress, or eliminate unwanted weeds.
What is the difference between selective and non-selective herbicides?
Selective herbicides target specific weeds without harming the crop, whereas non-selective herbicides destroy all exposed green vegetation.
What does pre-emergence herbicide application mean?
Pre-emergence application means applying the herbicide to moist soil after sowing the crop but before the weeds or crop seedlings germinate.
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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