Pesticides used to eliminate or control the growth of weeds are known as herbicides. The beginning of chemical weeding farmland can be traced back to the end of the nineteenth Century, Europe in the prevention and control of grape downy mildew, occasionally found Bordeaux can hurt some cruciferous weeds without harming cereal crops; France, Germany, the United States also found that the herbicidal activity of sulfuric acid and copper sulfate etc., and used for wheat weed. Organic chemical herbicides began in 1932 during the discovery of selective herbicide dnoc. In 1940s, the emergence of 2 4- drops greatly promoted the rapid development of the organic herbicide industry. The synthesis of glyphosate in 1971 was a major breakthrough in organophosphorus herbicides, with the characteristics of broad grass killing spectrum and no pollution to the environment. In addition to the emergence of a variety of new dosage forms and new use techniques, the effect of weeding is greatly improved. In 1980, the world's herbicide accounted for 41% of the total pesticide sales, and was the first to exceed the pesticide. Since then, the development of herbicides in the world has been developing steadily. The development of high efficiency, low toxicity, wide spectrum and low dosage varieties is becoming more and more important.
Herbicides can be classified in many aspects, such as the mode of action, the location of the drug and the source of the compound. Plant sodium chlorate, borax, arsenate, three trichloroacetic acid for any species are dead, but because these are residual effects, so can not be used in fields. Selective herbicides especially the majority of nitro phenol, chlorophenol, amino acid derivatives are effective, including O- -N- isopropyl phenyl carbamate [O-isopropy-N-phe-nylcarbamate, abbreviation IPC:C6H5NHCOOCH- (CH3) 2], two nitro -O- (sodium dinitro-O-cresylate) and sodium cresol. The most famous herbicide containing herbicide is 2, 4-D. It is believed that it can disrupt hormone balance and physiological disorder in plants, but it is a very effective herbicide for plants other than Gramineae. It is generally believed that this selectivity is determined by the strength of plant species to 2 or 4-D detoxification, or the concentration of 2 and 4-D varies according to plant species.