Soil Persistence of Tebuthiuron in the Claypan Resource Area of Texas

Abstract

Pelleted tebuthiuron { N -[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl] - N,N ′-dimethylurea} was applied aerially on duplicate plots at 2.2 and 4.4 kg/ha in spring, summer, fall, and winter of 1978 and 1979. Treatments were made near Bryan in the Claypan Resource Area of Texas on an area supporting a stand of mixed brush consisting mostly of oak ( Quercus ) species. Soils were sampled at eight locations in each plot at depths of 0 to 15 and 15 to 30 cm in March 1980. Bioassays using ‘Tamcot’ cotton ( Gossypium hirsutum L.) and ‘Caddo’ wheat ( Triticum aestivum L.) were done in the greenhouse to detect levels of tebuthiuron residues in the soil. A standard curve was developed to compare known concentrations of tebuthiuron to the unknown content from treated plots. Tebuthiuron persisted in all treated soils and ranged from 0.08 to 0.49 μg/g. Concentrations were usually greater in soil treated in 1979 than in 1978 and in soil treated with 4.4 kg/ha of tebuthiuron than 2.2 kg/ha. No consistent differences in tebuthiuron residues existed either between soil depths or among seasons of application using the bioassay.