Studies on Residual Dynamics of Pymetrozine in Rice

[Objective] The study aimed to understand the residual dynamics of pymetrozine in rice and its final residual amount in rice in the harvest.[Method] Field trial and high performance liquid chromatography were carried out to study the degradation dynamics of 25% pymetrozine WP in rice plant and its final residue amount in rice in the harvest.[Result] The degradation half-life of pymetrozine were 0.51-0.53 d in the rice plant,which accorded with the dynamic equation of first-order chemical reactions.When the rice was sprayed one time with 25% pymetrozine WP in the growth stage according to the recommended dosage of 300 g/hm2 and high dosage of 600 g/hm2,the final residues of pymetrozine in rice straw,rice shells and rice were all below the limit of quantification at harvest time.[Conclusion] The pymetrozine is a easily degradable pesticide(half-life30 d).When the rice was applied with 25% pymetrozine WP,the recommended dosage of 300 g/hm2 was suggested to apply in the rice one time.The MRL of pymetrozine in rice may be suggested to be 0.02 mg/kg temporarily.