Analysis of Particle Size Regulating the Insecticidal Efficacy of Phoxim Polyurethane Microcapsules on Leaves

The size of microcapsules (MCs) is an important and easily adjustable parameter; however, the function of this parameter in the movement behavior of pesticide MCs had not yet been studied. Phoxim-loaded polyurethane MCs with three various size distributions (average diameters of 1.39 μm, MC-S; 5.78 μm, MC-M; and 23.60 μm, MC-L) were obtained. In the greenhouse experiment, the insecticidal activities of MC-S and MC-M occurred mainly in the first 3 days and that of MC-L was maintained from 3 to 10 days after application. The direct and secondary distributions of a pesticide were defined and used to investigate the effects of particle size on the insecticidal activity of MCs in the field. The results indicated that the reason why MC-S had an excellent initial activity was that it was more widely distributed on the surface of the organism, was more likely to be adhered to by pests, and had greater resistance to rain washing. MC-L had excellent later-stage insecticidal activity, which was mainly because of its...