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.
