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CHEMICAL CLASSIFICATION OF HERBICIDES
CHEMICAL CLASSIFICATION OF HERBICIDES |
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Prior to the widespread use of chemical herbicides, mechanical control and cultural controls, such as altering soil pH, salinity, or fertility levels were used to control weeds.
The first widely used herbicide was 2,4-dichlorophenoxyacetic acid, often abbreviated 2,4-D which kills many broadleaf plants while leaving grasses largely unaffected (high doses of 2,4-D at crucial growth periods can harm grass crops such as maize or cereals). The low cost of 2,4-D has led to continued usage today and it remains one of the most commonly used herbicides in the world. In 1950s triazine family of herbicides, which includes atrazine was introduced. Atrazine does not break down readily (within a few weeks) after being applied to soils of above neutral pH. Atrazine is said to have carryover, a generally undesirable property for herbicides. Glyphosate, frequently sold under the brand name Roundup, was introduced in 1974 for non-selective weed control. It is now a major herbicide in selective weed control in growing crop plants due to the development of crop plants that are resistant to it. Many modern chemical herbicides for agriculture are specifically formulated to decompose within a short period after application. This is desirable as it allows crops which may be affected by the herbicide to be grown on the land in future seasons. However, herbicides with low residual activity (i.e., that decompose quickly) often do not provide season-long weed control. List of herbicides with their common name and chemical name
LOW VOLUME HERBICIDES Herbicides play an important role in weed control on agricultural and non agricultural surfaces. They are mainly applied by sprayers (foliar application) that consist of a herbicide tank, a pressure generator, spray nozzles, pipes and connectors. Foliar application of herbicides entails spraying the leaves of target plants during the growing season with a low concentration of herbicide in a water carrier. Among all possible weed control methods, the use of herbicides is principally associated with risks for human health and the environment. Because of this there is much discussion about the use of herbicides. Reduction in use of herbicides will reduce associated risks. It is expected that herbicide use can be much reduced when herbicides are applied according to best possible practices i.e. application of minimal doses of herbicide adjusted to weed, weather, herbicide and sprayer conditions. Low volume herbicide application has many benefits. Besides its cost-effectiveness for the landowner, the low volume solution is also environmentally friendly. The spray can be applied with a hand-powered, backpack sprayer or larger, motorized sprayers. This type of application method has numerous advantages:
HERBICIDE MIXTURES It involves mixing of two or more herbicides used for effective and economical weed control. Advantages of Mixture
1. Tank mixtures made with the desired herbicides and rates before application e.g., Anilophos + 2,4-D EE – rice 2. Ready mix – formulated by the manufacturer. Ready mix available in the world market e.g., 2,4-D+Glyphosate, Paraquat+2,4,-D, Atrazine+metolachlor, paraquat+oxyfluorfen. HERBICIDE ROTATION The practice of following a systematic, rotational sequence of herbicide used in the same field to prevent or control formation of herbicide resistant weeds. In a rotational programme a soil-applied or foliage applied herbicide or both are used in a sequence to take care of annual as well as perennial weeds. The choice of herbicide depends on the tolerance of crops to particular herbicides, type of weed spectrum, intensity of weed infestation, soil and climatic factors etc., The best rotational programme will aim at maximum cumulative cost benefit ratio and least residual problems and least build-up of tolerant weeds. Advantages
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