Table of Content
Learn in Brief{Click on Me}
Learn in Hindi
Herbicide is a chemical substance used specifically to kill or inhibit the growth of unwanted plants, particularly weeds. The effectiveness of chemical weed control largely relies on the selective nature of herbicides, which allows them to target and eliminate weeds without causing significant harm to the crops.
The principles of chemical weed control are grounded in the selectivity of certain herbicides towards weeds while sparing the cultivated crops. This selectivity is influenced by several factors:
- Morphological Differences: Structural differences between the crop and weed plants.
- Differential Absorption: Variations in how the plants absorb the herbicide.
- Differential Translocation: Differences in how the herbicide moves within the plant system.
- Differential Deactivation: Variations in the ability of plants to deactivate the herbicide.
Herbicides can be classified based on their method of application, mode of action, and mobility.
- Soil-Applied Herbicides: These herbicides act primarily through the root and other underground parts of the weeds. For example, Fluchloralin.
- Foliage-Applied Herbicides: These herbicides are mainly active on the plant's foliage and are absorbed through the leaves. Examples include Glyphosate and Paraquat.
- Selective Herbicides: These herbicides kill specific weed species without affecting the crop plants. For example, Atrazine selectively targets certain weeds without harming crops like maize.
- Non-Selective Herbicides: These herbicides destroy almost all vegetation in the treated area. An example is Paraquat, which is highly effective but non-selective.
- Contact Herbicides: These herbicides kill only the parts of the plant that they directly contact. Paraquat is a typical example, effective in destroying the above-ground parts of plants.
- Translocated Herbicides: These herbicides move within the plant, usually from the point of application to other parts, including roots or growing points. Glyphosate is a translocated herbicide that moves through the plant's vascular system, making it effective in killing perennial weeds.
Pre-Plant Application (PPI): Application of herbicides before the crop is planted or sown. Soil application as well as foliar application is done here. For example, fluchloralin can be applied to soil and incorporated before sowing rainfed groundnut while glyphosate can be applied on the foliage of perennial weeds like Cyperus rotundus before planting of any crop.
Pre-Emergence: Application of herbicides before a crop or weed has emerged. In case of annual crops, application is done after the sowing of the crop but before the emergence of weeds, referred to as pre-emergence to the crop. In perennial crops, it is pre-emergence to weeds. Eg. Atrazine, Pendimethalin, Butachlor, Thiobencarb, Pretilachlor
Post-Emergence: Herbicide application after the emergence of crop or weed. For example, spraying 2,4-D Na salt to control parasitic weed striga in sugarcane is called post-emergence. Eg. Glyphosate, Paraquat, 2,4-D Na Salt
Early Post-Emergence: Another application of herbicide in slow-growing crops like potato, sugarcane, 2-3 weeks after sowing.
Inorganic Compounds
Organic Compounds