Pesticide persistence beyond the critical period for control leads to residue problems . 农药一旦超过控制的临界期，就会导致残留问题。
2.
( 3 ) with the development of arrangement of agricultural industries structure and the expansion of intensive manufacturing scale the traditional veterinary pharmaceuticals are not able to satisfy the agricultural modernization and the drug residue in animal products get extensive attention from the society . therefore it ' s imperative to develop new kinds of veterinary pharmaceuticals with higher efficacy and lower toxicity 三是随着农业产业结构调整的进程，集约化生产规膜的不断扩大，传统的兽药已不能适应农业现代化的需要，动物源产品的药物残留问题已引起社会的广泛关注，开发高效低毒的新兽药的需求日益迫切。
