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A farmer sprays his grape vines with pesticide. Agrochemicals are chemicals that are used in agriculture—either in the growing of crops or the raising of livestock. Pesticides protect plants from weeds, diseases and pests. Fertilizers give extra nutrients to plants. Hormones, medicines and other chemicals are given to plants and animals to control their growth. Some agrochemicals come from natural sources, but most are synthetic (manmade) and are produced in chemical plants. Natural fertilizers such as manure or peat are not agrochemicals. Farms that do not use synthetic agrochemicals are called organic farms. Many agrochemicals are toxic (harmful or poisonous). Most countries have regulations about the use and storage of agrochemicals. 

Maize and weeds before and after herbicide spraying. In the top photo, the maize (centre) and weeds (to the left) have just been...Read More >>Maize and weeds before and after herbicide spraying. In the top photo, the maize (centre) and weeds (to the left) have just been sprayed with a glysophate herbicide. In the bottom photo, taken two weeks later, the herbicide has killed the weeds, while the maize has flourished. Glysophate is made from chloroacetic acid, which is itself made by reacting chlorine with acetic acid.


Pesticides are developed to target and kill particular weeds, plant diseases and pests (such as fungi, insects, mites, rodents or snails). They are often sprayed on to crops, using planes, tractors or hand-held machines. A commonly used group of chemical pesticides is herbicides (weed-killers) made from phenoxy acid. Phenoxy acid is made from the chemical phenol, which is made from cumene, which is itself obtained from petroleum. Phenoxy herbicides kill broad-leafed weeds without affecting grasses, such as cereal crops. They work by making the weeds grow abnormal cells, stopping their ability to transport nutrients.

Fertilizer use began in the ancient world, with the ancient Mesopotamians using manure and fish guts on their fields at least 7000 years ago.

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