Pests cost thousands of millions of dollars annually in lost agricultural production, and at least 10 percent of the harvest is destroyed, mainly by rodents and insects, while in storage. In 1970, one-sixth of the United States' maize crop was devastated by disease. Later that decade, Java lost 70% of its rice crop to brown planthoppers. Some $1,600 million is spent annually by the world's potato farmers so as to combat the fungus that caused the Irish potato famine of the 1840s.Pesticide 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. However, contamination of both food and environment can be caused by inappropriate and excessive use and, in some cases, the health of fanners is damaged. The natural enemies of pests are also killed by pesticides. This allows the pests to multiply. Meanwhile, the number of pest species with resistance to pesticides has increased from a handful 50 years ago to over 700 now (these include 520 insects and Ite S 130 plant species and 113 weeds).biological controls, such as the use of pests' natural enemies, are useful. In West africa, the introduction of a wasp has brought about 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. Some new discases-resistant varieties of plants have been developed. Several genes are often used from wild varieties with inbuilt diselse resistance. However, it has been found that pests and diseases often mutate into a forth capable of attacking the new plants. When this happens, the researchers must then deNetop plants with resistance to the mutated pests and diseases. This is a never-anding process. Both pesticides and biological controls can be expensive: pests become increasingly resistant to chemicals. and the genetic resistance of plants needs to be renewed regularly by the plant breeder. Integrated Pest Management (IPM) combines a variety of controls including the conservation of existing natural 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.
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