pesticide

A vineyard in San Leo, Italy, being sprayed with pesticide to control mildew or virus diseases that can attack the vine. Pesticides protect against insect damage, weeds, fungi, and other pests, but can cause problems when they remain in the food chain.

Crop dusting: spraying crops with insecticide and pesticide from an aeroplane. Spraying the crops in this way allows a large area to be sprayed quickly and also avoids having to drive vehicles through fields, thus potentially damaging the crops.

Any chemical used in farming, gardening, or in the home, to combat pests. Pesticides are of three main types: insecticides (to kill insects), fungicides (to kill fungal diseases), and herbicides (to kill plants, mainly those considered weeds). Pesticides cause a number of pollution problems through spray drift onto surrounding areas, direct contamination of users or the public, and as residues on food. The World Health Organization (WHO) estimates that thousands of people die annually worldwide from pesticide poisoning.

The safest pesticides include those made from plants, such as the insecticides pyrethrum and derris. Pyrethrins are safe and insects do not develop resistance to them. Their impact on the environment is very small as the ingredients break down harmlessly.

More potent are synthetic products, such as chlorinated hydrocarbons. These products, including DDT and dieldrin, are highly toxic to wildlife and often to humans, and their use is now restricted by law in some areas and is declining. Safer pesticides such as malathion are based on organic phosphorus compounds, but they still present hazards to health. An international treaty to ban persistent organic pollutants (POPs), including pesticides such as DDT, was signed in Stockholm, Sweden, in May 2001. The United Nations Food and Agriculture Organization reported in the same month that more than 500,000 tonnes of pesticide waste resides in dumps worldwide.

Pesticides were used to deforest Southeast Asia during the Vietnam War, causing death and destruction to the area's ecology and lasting health and agricultural problems.