Persistence of Mepronil in Rice Plants Treated with Two Formulations of the Fungicide

Abstract

The persistence of and the factors related to the decrease of mepronil fungicide in and on rice plants treated with 2 formulations of the chemical, a dust and a wettable powder, were studied for two years. When mepronil was applied at the young panicle formation and the booting stages of rice plants, it adhered to the aerial parts, especially to the leaf blades, at a high concentration. The concentration decreased rapidly within 14 days after application and gradually thereafter. The initial concentration of mepronil in plants immediately after application was somewhat larger when it was applied in the form of a wettable powder rather than as dust. The rate of decrease did not differ largely whether the dust or the powder was used. When the factors affecting the disappearance of mepronil on rice plants were investigated using a complex exponential decay equation, the rapid decrease of mepronil at the early stage after application was presumed to be attributable to the elimination of mepronil from the surface of the plants, and the gradual decrease during the late stage was presumed to be due to the metabolism of the fungicide in plants. © 1984, Pesticide Science Society of Japan. All rights reserved.