Dissipation of Thiobencarb Concentration in Soil Solution under an Upland Field Condition and Its Herbicidal Activity

Abstract

An emulsifiable concentrate of thiobencarb, S-(4-chlorobenzyl) diethylthiocarbamate (active ingredient: 50%, Saturn^®), was applied at 15kg a. i./ha to an upland field just after sorghum (Sorghum bicolor) sowing. Thiobencarb concentration in soil solution and centrifuged soil began to decrease 7 days after application (DAA) in 0-5cm from the soil surface. The ratio of thiobencarb concentration between the soil solution and the centrifuged soil was about 2% at 0DAA and decreased to ca. 0.4% at 11DAA. Sorghum growth was suppressed within 2 weeks in the field. In the laboratory, sorghum sensitivity to thiobencarb was closely related to the initial concentration in the soil solution of 0-1cm from the soil surface, in which most thiobencarb was distributed. Consequently, it was supposed that herbicidal activity of soil-applied thiobencarb on sorghum was largely dominated by the initial concentration in soil solution in the soil surface under an upland field condition.