herbicide

Herbicides are also known as herbicides or herbicides. It refers to a chemical agent used to remove farmland weeds but is generally harmless to crops. The most widely used and most important is organic herbicides, and the use of herbicides is one of the important measures for modern agricultural chemicalization. At the end of the 19th century, in the prevention and treatment of European grape downy mildew, it was discovered by chance that Bordeaux mixture could damage some cruciferous weeds without harming cereal crops. At the end of the 19th century, France, Germany, and the United States discovered the herbicidal action of sulfuric acid and copper sulfate, and used it for weeding in wheat and other places. This is the beginning of chemical weeding in farmland. In 1932, the organic selective herbicide dinitrophenol was discovered and began to enter the period of organic chemical herbicides. In the early 1940s, 2,4-D was chemically synthesized and used for weeding in the field. It has high biological activity, strong selectivity, wide herbicidal spectrum, and obvious herbicidal effect. Under the influence of 2,4-D, it greatly promoted organic The rapid development of the herbicide industry. In the 1950s, various types of organic herbicides were developed, such as aniline and chlorpheniramine, which are carbamates; acetophan, chlorpyrifos, ketodan, etc.; Benzene simazine, atrazine, etc.; benzoic acid-based Bean kewei; Substituted urea-based diuron. In 1959, the chemical weeding area in the United States reached 21 million hectares. Since the 1960s, most of the new varieties of pesticides have been developed as herbicides, such as diflunarin-based trifluralin; amide-based propanil, alachlor, thiocarbamate, and wheatgrass , grass dandan; diphenyl ether herbicide ether, oxalic acid ether, etc., and mainly soil treatment agents. The emergence of a large number of highly efficient and selective herbicides has led to changes in farming systems. In the 1970s, the concept of Integrated Weed Management System (IWMS) was proposed in the United States, but its core is still chemical weeding. In 1971, Monsanto Company of the United States synthesized glyphosate, which has a wide spectrum of herbicides and no pollution to the environment. It is a major breakthrough in organic phosphine herbicides. Combined with the emergence of a variety of new dosage forms and new use technologies, the herbicidal effect is greatly improved. The mechanism by which herbicides can remove weeds and is harmless or less invasive to crops is complex. It is generally believed that there are three mechanisms: 1 using different physiological characteristics of weeds and crops for certain drugs. For example, simazine can be used for weeding in corn fields, because corn contains a detoxifying substance that can decompose simazine, as long as the absorption is not too much, it will not affect its growth. However, the weeds in the corn field do not contain this detoxifying substance, and are easily killed by a small amount of simazine to achieve herbicidal purposes. 2 The opportunity to use drugs to contact or stick to various plants is different. For example, kerosene is a potenticide that kills various plants, but the leaves of the onion are conical and erect, and there is wax on the outside. The sprayed drops can't be used, so the kerosene can be sprayed on the onion floor to remove the weeds. . Generally, the narrow leaves are less medicinal than the broad leaves, and the erected leaves are less affected than the transverse ones, and the deep roots are less medicinal than the shallow roots. 3 The ability to be absorbed by plants is different. The epidermis of various plants has different protective tissues, and the degree of absorption of the medicament after spraying on the epidermis is different. The epidermis is thick and waxy and does not easily penetrate into the medicine, so it will not be harmed. The mechanism of action of herbicides is not the same, but in general, it inhibits, hinders or interferes with physiological and biochemical processes of plants such as respiration, photosynthesis and synthesis of living substances, so that they cannot grow normally and cause death. In recent years, various poisoning mechanisms have been extensively studied to synthesize more new herbicides with high efficiency, low toxicity and strong selection. International herbicide use accounts for 40% of total pesticides, and China only 10-20%. The use of herbicides should pay attention to accurately grasp the concentration, dosage and application period, otherwise it will cause serious phytotoxicity of crops, causing crops to grow abnormally and even wither and die. Some varieties are toxic to fish and shellfish; their use as soil treatment can affect the reproduction of soil microorganisms. Long-term use of a herbicide can also cause resistance to grass damage. The application of chemical herbicides brings great social and economic benefits, but some also produce different degrees of phytotoxicity to crops (especially the ultra-efficient herbicides such as sulfonylureas that have been developed and applied in recent years. Changes in the phytotoxicity of the crops and the weed population, resulting in varying degrees of economic loss. To this end, domestic research and development of new varieties, while strengthening the research and development of herbicide compound preparations. Of the more than 90 Chinese patents on herbicides applied for in China from 1996.8 to 1997.7, more than 80 were patents on compound herbicides. In addition, in-depth studies on herbicide antidote, synergist, herbicide action mechanism, selectivity principle and rational use technology are underway.