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目前适用于美国杂草防除的几百种商品除草剂中,有效成分约有150种化合物。每种除草剂在销售使用前,须对选择性、作物耐药性、在土壤中的持久性和迁移、残留以及毒理、环境影响作全面评价。一种化学药品若伤害作物,就不是有用的除草剂,所以不予注册。同样,若一种除草剂残存于土壤中,并伤害后茬轮作作物的生长时,就不能登记为轮作作物的除草剂。但是,施用过高剂量、不适当或违章施药、雾液的飘移、除草剂蒸气的迁移以及反常的土壤和气候条件,都可以引起药害。
Of the hundreds of herbicides currently available for weed control in the United States, the active ingredient has about 150 compounds. Each herbicide should be evaluated for its selectivity, crop resistance, persistence and migration in soil, residues, and toxicological and environmental impacts prior to its sale. A chemical that injures a crop is not a useful herbicide and is therefore not registered. Similarly, a herbicide can not be registered as a herbicide for crop rotation if it remains in the soil and harms the growth of crop rotation crops. However, phytotoxicity can result from overdosage, inappropriate or illegal application, drift of fog, migration of herbicide vapors, and abnormal soil and climatic conditions.