How to use herbicide safely

Herbicides are classified into selective herbicides and non-selective or herbicidal herbicides according to their ability to identify crops and weeds.
In some books, the selectivity of herbicides is divided into six categories: position selectivity, time difference selectivity, morphological selectivity, physiological selectivity, biochemical selectivity, and protective substances or safener selectivity. In fact, this has the selectivity determined by the characteristics of the drug itself, and the different application methods and effects for crop and weed differences. It should be a selective use technique.
Let's talk about non-selective herbicides, also called killer herbicides. The masses are called "one sweeping light." Glyphosate, paraquat (chlorine), sodium pentachlorophenol, etc. can only be used when there is no crop in the field, and can be sown or transplanted after the agent is inactive. It should be noted that the speed of these herbicides is reduced, and the temperature is often reduced when the temperature is high, the soil does not retain water, and the rainfall is slow. In fact, this is already the difference in the time to start using crops and weeds, and it is also a technique that uses time difference selection.
If the difference in the distribution of crops and weed seeds and roots in the soil is used, the agent is spread on the surface of the soil by 1 to 2 cm, which can kill or inhibit the weed seeds that can germinate in the shallow layer, while the crops (such as wheat) or fruit trees The roots are deep and unaffected. For example, after soy sowing, alachlor (lace) is used before sowing, and corn, cotton, soybean, peanut, wheat and other crops are pre-emerged with acetochlor after sowing. It should be noted that in the soil sand, the organic matter content is low, in the case of rainfall or the formation of stagnant water, the agent may penetrate downwards, prone to phytotoxicity. Seeds that are sown shallower, such as some vegetable fields, are not suitable for use with such agents. By the same token, if you are spraying paraquat in an orchard, you must choose a windless weather, preferably when the airflow rises in the afternoon is not obvious, so that the weeds sprayed onto the ground by the medicament will not drift to the leaves of the fruit trees. Or outside the orchard.
The third is to use the difference in morphology of crops and weeds, typically using 2,4-butyl butyl ester. The drug is a hormone-selective herbicide. The low concentration has a stimulating effect on plant growth, and the concentration is high and inhibits or even kills. One of its selective weeding effects is that the growth points of the grass crops are covered by layers of leaves, while the growth points of the dicotyledon weeds are always exposed. Thus, under the same spraying conditions, the growth point of the dicotyledonous weeds is higher, which causes distortion or inhibition. When using such a drug, pay attention to the application time. It is not advisable to use the drug before and after the jointing of the wheat. Otherwise, the wheat will also form a deformed ear. It is also necessary to spray the windless weather to prevent the pesticide from drifting to the surrounding vegetables or melons and fruit fields. After spraying, the equipment must be carefully cleaned to avoid affecting other farmland.
Like the use of props in rice fields, it is due to the difference in the biochemical reactions of the chemicals in rice and alfalfa. Rice can rapidly hydrolyze the enemy, which is arguably true selectivity. Similar herbicides such as rice Honda use He Da Zhuang, corn fields use simazine and atrazine, soybean fields use fensulfuron, and carrot fields use trifluralin. They are safe to use in the appropriate fields, but they can be plagued by the wrong field or excessive residue.
Author: China Agricultural University Professor Xiao Yue Yan
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