I. Based on time of application:
Pre planting: Herbicides are applied before the crop is planted.
Herbicide with greater toxicity on emerging crop seedlings are usually before crop is planted. Pre emergence: Herbicides are applied before a crop or weeds have emerged. Post emergence: Herbicides are applied after the emergence of weed or crop.
II.Based on mode of activity: Systemic or translocated herbicide:
Herbicides that are translocated throughout the plant system and brings the activity at a place distant from the point of application Contact herbicide: Herbicide that kills the plant part that comes in contact with it. Little movement from point of application
III.Based on selectivity:
1. Selective herbicide: Kills only the target plant species (weeds) in a mixed plant population ( crop plants and weeds).
2. Non selective herbicides: kills all the plants that come in contact with the herbicide.
IV: Based on Placement:
1. Soil applied: When applied to soil.
2. Foliage applied: When applied on the foliage of weeds.
V: Based on chemical group:
- Aliphatics - Amides and acetamides: eg. Alachlor and Butachlor
- Arsenicals - Benzoics and phenyle acetates
- Bipyridiliums - Carbamates & Carbanilates
- Dinitroanilines: e.g. Oryzalin, Pendimethalin, Trifluralin
- Diphenyle ethers: e.g. Nitrofen, Oxyfluorfen
- Phenoxyacids: e.g 2,4-D - Pyridazinones.
- Thiocarbamate: e.g. Benthiocarb.