Dissipation Kinetics and Risk Assessment of Thiamethoxam 25 % WG Residues in Vegetable Cowpea

A field experiment was conducted to study the rate of dissipation of thiamethoxam 25% WG in vegetable cowpea. Thiamethoxam 25%WG @ 0.24 ml l-1 was sprayed at pod formation stage, and samples of pods were harvested at 0 (2 hr after spray), 1, 3, 5, 7, 10, 15 days after spray. Residues were estimated using liquid chromatography tandem mass spectrometer (LC-MS/ MS) at the All-India Network Project on Pesticides Residues, College of Agriculture, Vellayani, Kerala. The mean initial residue was found to be 0.53 μg g-1, and residues were observed persisting up to three days and reached below quantification level on fifth day.