If the concentration of pesticides is too high, or the dosage is too large, or the use period is not suitable, it will cause chemical damage to plants. Phytotoxicity can be divided into acute toxicity, chronic toxicity and residual toxicity. The symptoms of acute phytotoxicity are obvious, which can be directly observed from the morphological changes of plants, such as burning spots, leaf curling, deformity, defoliation, flower dropping, fruit dropping, withering, perforation, loss of green, slow growth, short plants, decreased germination rate, bud death and even adult death. The symptoms of chronic phytotoxicity are not obvious, and it is difficult to observe obvious changes only from the morphology of plants, which is also called recessive phytotoxicity. It can only be judged by comparing it with uninjured healthy plants. Generally, it is characterized by poor growth and development, which ultimately affects the yield and quality of crops. Residual phytotoxicity mainly refers to the residue of pesticides or their bioactive degradation products applied in soil. Although the application of pesticides is not harmful to the current crops, it will affect the sensitive crops next year. Sometimes crops do not show phytotoxicity at the first application, but after repeated use or years of application, the long-term accumulation of pesticide residues in the soil will reach the level of phytotoxicity to this crop.