Correlation between the accumulation amount of clothianidin in cucumber leaves and the control efficacy on greenhouse whitefly and the dynamics of residue dissipation

In order to provide theoretical basis for guiding scientific use of 18% clothianidin embedding GR and reducing environmental risk, the correlation between the accumulative amount and the control efficacy on whitefly of 18% clothianidin embedding GR and the dynamics of residual dissipation were investigated on greenhouse cucumbers. Under greenhouse conditions, using 1% clothianidin GR as the control agent, the control efficacy of 18% clothianidin embedding GR on whitefly was investigated. An ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was established for the determination of clothianidin residues in cucumber leaves and soil. The accumulative amount of clothianidin in cucumber leaves at different application dosages and different growth stages was determined, and the correlation between the accumulative amount and control efficacy was studied. The results showed that the control efficacy of 18% clothianidin embedding GR on whitefly was 49%-95%, which was 1.16-2.32 times higher than that of 1% clothianidin GR, and the ideal control efficacy of 18% clothianidin GR granules could be achieved at 450 g a.i./hm². The residue dissipation dynamic of clothianidin in soil was in accordance with the first-order kinetic equation. The half-life of 18% clothianidin embedding GR was 43-63 days, while that of 1% clothianidin GR was 35 days, which showed that 18% clothianidin embedding GR had a slow dissipation rate in soil. The accumulative amount of clothianidin in cucumber leaves increased with the increase of the dosage of 18% clothianidin embedding GR. Both the cumulative amount and the control efficacy on whitefly showed a trend of first increasing and then decreasing with the passage of the time after application, and reached the highest value on 56th days after application. When the application rates of active ingredients were 450, 600 and 750 g/hm², the maximum accumulation of clothianidin in upper leaves of cucumber were 1.9, 2.2 and 2.8 mg/kg, respectively, and the highest control efficacy were all 90%. The maximum accumulation of clothianidin in middle leaves were 2.2, 2.5 and 3.0 mg/kg, and the highest control efficacy were 94%, 93% and 95%, respectively.