Deposition, Distribution, Metabolism, and Reduced Application Dose of Thiamethoxam in a Pepper-Planted Ecosystem

Abstract

To decrease the application dose of thiamethoxam (TMX) to control the pepper whitefly (<i>Bemisia tabaci</i> Q), the deposition, dissipation, metabolism, and field efficacy of TMX were investigated in a pepper (<i>Capsicum annuum</i> var. <i>grossum</i>)-planted ecosystem using eight types of nozzles at six concentrations (56.25, 41.25, 26.25, 21.0, 15.75, and 10.5 g a.i./hm²). The initial deposition amount of TMX in the pepper plant first increased and then decreased with increasing application dose. The optimum spray conditions of TMX were found to be a droplet size of 200 μm volume median diameter and a spray volume of 350 L/hm². Moreover, three metabolites, TMX-dm, clothianidin (CLO), and C₅H₈O₂N₃SCl, were detected in the pepper-planted system. The dissipation rate of TMX in the pepper-field ecosystem was leaves > stems > fruits > roots > soils. The results revealed the deposition and fate of TMX in the pepper-field ecosystem, and the application dose could be reduced by 20% based on the minimum recommended dose for controlling pepper whitefly.