Pesticide is a generic term that covers a wide range of natural and synthetic chemicals (over 700 in total) that are used to protect crops from attack from pests, both before and after harvest. There are many different sorts of pests. The term includes insects, slugs and snails, nematode worms, mites, rodents, weeds, molds, bacteria and viruses. The chemicals can be applied before and during growth of the plant or on to the stored crop as, for example, fumigants, which are used to kill pests that have infested stored cocoa or grain. Chemicals used to treat pests on animals are not included; they are considered as veterinary medicines.
The pesticide formulation used by the farmer will include the pesticide chemical itself and a number of other chemicals that enable it to be applied and to work as effectively as possible. These will include solvents, adhesives, and surface-active agents such as emulsifiers. In some cases other chemicals, known as 'safeners,' are applied to minimize the damage done to the crop while maintaining the effectiveness of the spray on the target.
It is estimated that worldwide usage of pesticides is around 2.5 million tons with a cost in 1997 of US$21 billion.
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