Determination of Residual Toxicity and Degradation Dynamics of Chlorfenapyr in Mulberry Leaves

In order to guarantee the safety for silkworm rearing when mulberry leaves sprayed with chlorfenapyr,the residual toxicity and degradation dynamics of chlorfenapyr in mulberry leaves during harvesting time were determined by methods of food intake and gas chromatography in this paper.The results showed that the period of residual toxicity of 250,200,150,100,and 50 mg/L chlorfenapyr sprayed on mulberry leaves were 5 d,5 d,3 d,1 d and 0 d,respectively.The degradation kinetics equation of 200 mg/L chlorfenapyr was C= 95.335e-0.159 9 t(R 2=0.906 8) in mulberry leaves and the half life time was 4.3 d.The minimum detectable concentration of this method was 3.97×10-4 mg/kg.At 2 h,1 d,3 d,5 d,7 d,14 d,21 d and 28 d after treated with chlorfenapyr at the concentration of 100 mg/L,the residues of chlorfenapyr in the mulberry leaves was 40.969,39.814,20.226,18.726,9.975,5.522,2.774 and 0.026 mg/kg,respectively.The final residues of the chlorfenapyr in the mulberry leaves at 21d after treated twice with the concentration of 200 mg/L or 100 mg/L was 12.958 mg/kg and 4.242 mg/kg,respectively.The above results suggested that the suitable concentration of 10% chlorfenapyr was 100 mg/L to control the pests in mulberry fields,and the mulberry leaf can be picked to rear silkworm at 5 d after treatment.