Persistence of Isoprothiolane in Paddy Water and Rice Plants after Submerged Applications

Abstract

Persistence of isoprothiolane in paddy water and rice plants was studied by submerging its 12% granules at various stages of growth. The concentration in paddy water reached a maximum of 3–8 ppm within 1–3 days, and then decreased rapidly with a half life of 4 days. However, that in the plants changed more slowly so that the peak concentration was obtained 3–11 days after the application. The peak level in the shoots of plants was, almost identical (4-8 ppm) when the granules were submerged. Therefore, the incorporated amount of the compound corresponds with the size of the plants. The compound then disappeared with a half life of about a month. However, the concentration in the shoots reduced more rapidly when dilution by new growth could accelerate it. After the panicles had headed, they progressively accumulated the compound. Their concentration was always lower than, but well related with, that in the other parts in which the compound was almost uniformly distributed. The residues in hulled rice and straws were nicely correlated with the number of days after application. These changes of isoprothiolane in rice plants should explain the residual effect against rice blast and planthoppers. © 1982, Pesticide Science Society of Japan. All rights reserved.