害虫、病菌和杂草是农业生产上的三大敌害。美国因病虫害而造成的农业减产,估计每年损失达一百五十亿美元,为其农业总产值(一九六七年,为四百四十亿美元)的三分之一。苏联每年损失为五十四亿卢布,为其总产值的百分之十三点六。一九六七年由于没有足够的化学农药防治,使世界各国的水稻产量损失达二千亿斤、甘蔗的损失达二亿 Pests, germs and weeds are the three major culprits in agricultural production. The reduction in agriculture in the United States due to pests and diseases is estimated to be $ 15 billion annually, a third of its total agricultural output ($ 44 billion in 1967). The Soviet Union lost 5.4 billion rubles a year, at 13.6% of its gross output value. In 1967, due to the lack of sufficient chemical and pesticide control, the output of rice in various countries in the world lost 200 billion kilos and the loss of sugarcane amounted to 200 million