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Fate and Effectiveness of Tebuthiuron Applied to a Rangeland Watershed¹

ABSTRACT

Tebuthiuron³ (N-[5-(1,1-Dimethylethyl)-1,3,4-triadiazol-2-yl]-N.N'-dimethylurea), a herbicide, was applied at a rate of 0.84 kg/ha to a rangeland watershed and test plots in pelleted and dissolved forms, respectively. The removal of tebuthinron in the runoff water from the watershed was determined for each runoff event. After 21 months, total tebuthiuron removed in runoff water was 0.47% of that applied. The low removal rate was credited to the timing of the tebuthiuron application. Tebuthiuron applied to test plots moved to a depth of 15 cm in 8 months with 326 mm of precipitation. Total tebuthiuron remaining in the test plots after 21 months was 38% of the amount applied. The time required for the concentration of tebuthiuron in the test plots to reach non-detectable levels was estimated to be from 2.9 to 7.2 years. Tebuthiuron was effective on the dominant species on the watershed 21 months after treatment, producing an apparent 100% kill for tarbush (Flourensia cernua DC.), fourwing saltbush [Atriplex canescens (Pursh) Nutt.], and littleleaf sumac (Rhus microphylla Engelm. ex Gray), and 61, 92, and 0% for creosote-bush [Larrea tridentata (DC.) Cov.], whitethorn (Acacia constricta Benth.) and graythorn (Condalia spathulata Gray), respectively.

Key Words: herbicide • brush control • water quality

¹ Contribution from the USDA-ARS, Southwest Rangeland Watershed Res. Center, Tucson, AZ 85719, in cooperation with Lilly Res. Lab.

² Soil Scientist, USDA-ARS; Research Specialist, Lilly Res. Lab., Tucson, AZ 85715; Hydraulic Engineer, USDA-ARS; and Hydrologist, Environ. Sci. Group LS-6, Los Alamos Natl. Lab., Los Alamos, NM, respectively.