Formulation Factors Affecting the Efficacy, Phytotoxicity and Rainfastness of Fenitrothion Microcapsules for Agricultural Use

Fenitrothion 20wt% microcapsules equal in mass median diameter (ca. 20μm) but different in wall thickness (T) were prepared and tested for efficacy against tobacco cutworms (Spodoptera litura), phytotoxicity to cabbage and rainfastness compared with a fenitrothion 50wt% emulsifiable concentrate. LC95 values of the microcapsules increased with increasing in T and there was an optimum range in T to maintain the efficacy for a long period. A way of action of the microcapsules against tobacco cutworms was supposed to be breaking by the insects. The microcapsules was less phytotoxic than the emulsifiable concentrate. The thicker the wall of the microcapsules, the lower the phytotoxicity. Microcapsules with a thin wall excelled the emulsifiable concentrate in rainfastness both immediately after spray and after drying.