农田杂草发生普遍,危害严重。据联合国农粮组调查,全世界每年因杂草危害,损失达204亿美元。以美国为例,每年因病虫草损失达120亿美元以上,其中病害占27%,虫害占28%,线虫占3%,草害占42%。国外有人从3000多个试验中得出结论:由于杂草的危害平均可降低农作物产量21%。我国1978年统计,全国有耕 The occurrence of farmland weeds is widespread and devastating. According to a survey conducted by the UN agriculture unit, the world every year due to weeds damage, loss of 20.4 billion US dollars. In the United States, for example, the annual loss of plant diseases and insect pests reaches more than 12 billion U.S. dollars, of which 27% are disease diseases, 28% are pests, 3% are nematodes and 42% are grass diseases. Someone from abroad has concluded from more than 3,000 experiments that on average the crop yield is reduced by 21% due to the weed damage. Statistics of China in 1978, the country has farming