Controlling pests



Pests threaten crops, livestock and humans. At least 520 insects and mites, 150 plant diseases and 113 weeds have become resistant to pesticides meant to control them.

Pests cost thousands of millions of dollars annually in lost agricultural production, and at least 10 percent of the world's harvest is destroyed, mainly by rodents and insects, while in storage. In 1970 disease devastated one-sixth of the United States' maize crop. Later that decade, Java lost 70 percent of its rice crop to brown planthoppers, while a 1976 outbreak of New World screwworm in Texas cost US$ 375 million. The world's potato farmers spend some US$ 1 600 million annually to combat the fungus that caused the Irish potato famine of the 1840s. Rinderpest, a killer disease which in the 1890s wiped out 80-90 percent of all cattle in sub-Saharan Africa is now the target of a coordinated Pan-African eradication campaign.

Pesticides help. Their use multiplied by a factor of 32 between 1950 and 1986, with developing countries now accounting for a quarter of the world's pesticide use. But inappropriate and excessive use can cause contamination of both food and environment and, in some cases, damage the health of farmers. Pesticides also kill the natural enemies of pests, allowing them to multiply; meanwhile the number of pest species with resistance to pesticides has increased from a handful 50 years ago to over 700 now.

Biological controls, such as the use of pests' natural enemies, are useful. In West Africa, the introduction of a wasp has brought about a spectacular control of the mealybug, thereby saving cassava, the basic food crop for millions of Africans. In India the seeds of the neem tree (Azadirachta indica) are used as a natural insecticide to protect crops and stored grain. Researchers have found that the active compounds can control over 200 species of pest, including major pests such as locusts, maize borers and rice weevils, yet do not harm birds, mammals or beneficial insects such as bees.

Scientists have developed new varieties of plants, often using genes from wild varieties with inbuilt disease resistance. Genes from the wild have been used to protect Brazil's coffee plantations, while a Mexican wild maize confers resistance to seven major diseases.

Both pesticides and biological controls can be expensive: pests become increasingly resistant to chemicals, and the genetic resistance of plants to pests needs to be renewed regularly by the plant breeder. Integrated pest management (IPM), now the basis of FAO plant protection activities, combines a variety of controls, including the conservation of existing nature enemies, crop rotation, intercropping, and the use of pest-resistant varieties. Pesticides may still continue to be used selectively but in much smaller quantities.

Five years after IPM was widely introduced in Indonesia, rice yields increased by 13 percent, while pesticide use dropped by 60 percent; in the first two years alone the Government saved US$ 120 million that it would have spent subsidizing the chemicals. In the Sudan, IPM produced good results with a more than 50 percent reduction in insecticide use. In the United States, a 1987 study found that apple growers in New York state and almond growers in California who used IPM substantially increased their yields.

Tsetse fly

Screwworm fly

Black tarantula

Pests and diseases have no regard for national borders. FAO's EMPRES programme is a major initiative for transboundary control of pests.


Species resistant to pesticides

Numbers of species resistant to pesticides


Worldwide locust distribution


Pesticide safety

FAO keeps countries informed of pesticides that are generally acceptable and helps to ensure that pesticides are properly labelled and packaged. It is also eliciting support for the destruction of the large stocks of hazardous pesticides that have built up in many developing countries. Most developing countries have neither the resources nor the expertise to rid themselves of these toxic and useless chemicals. FAO puts the quantity of obsolete pesticides in Africa alone at 20 000-30 000 tonnes, which will cost up to US$ 150 million to destroy.


Controlling the desert locust

Severe locust plagues in 1987-89 were mainly fought with chemical pesticides. Since then, environmental concerns have necessitated the development of alternative strategies.

Desert locusts (Schistocerca gregaria) have swept over Africa, the Middle East and western Asia for millennia. Under particularly favourable breeding conditions numbers can reach plague proportions. Often assisted by winds, swarms of 400 million or more insects, each one able to eat its own weight in vegetation every day, travel great distances at bewildering speed, and can strip entire areas of crops.

FAO began its Locust Control Programme in 1952, and has been at the centre of attempts to combat outbreaks ever since. It runs the Desert Locust Information Service which provides early warning to affected countries and international donors.

In 1994 FAO set up the Emergency Prevention System for Transboundary Animal and Plant Pests and Diseases (EMPRES); its initial priorities were to improve management of desert locusts and eradicate rinderpest worldwide. It looks at ways to target locusts without affecting other life, including non-chemical means.


Change in pesticide use