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Tebuthiuron Distribution in Soil following Application of Pellets¹

ABSTRACT

Persistence, activity, and distribution of tebuthiuron {N-[5-(1,1 dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea} in two soils were studied following application of 40% active ingredients (a.i.) extruded pellets. Tebuthiuron dissipation from the surface 3 cm and within 2 cm of the point of pellet placement was best explained by the nonlinear regression equation: Y = bX^a, where Y is the tebuthiuron concentration in milligrams per kilogram, b is 7.05 x 10⁶, X is time (d) after pellet placement, and a is –2.272 (^r2 = 0.97). Applications of 40% tebuthiuron pellets at 0.6 or 1.1 kg ha^–1 left a detectable residue on 9 to 21 and 17 to 38% of the treated areas, respectively. The lower percentages were on a loam soil with 47 g kg^–1 soil organic carbon (OC) content and the higher percentages were on loam soils with 17 and 18 g kg^–1 OC. Crested wheatgrass [Agropyron cristatum (L.) Gaertn.] seedling growth was reduced 50% (GR₅₀) by tebuthiuron concentrations of 0.04 to 0.20 mg kg^–1, depending on soil OC content. Two years after application of 0.6 kg ha^–1, 40% tebuthiuron pellets to a big sagebrush (Artemisia tridentata Nutt.) community, with a loam soil that had a 30% shrub cover (17 g kg^–1 OC in interspaces and 48 g kg^–1 OC under former shrub canopies), <20% of the surface soil contained the crested wheatgrass GR⁵⁰.

Key Words: Bioassay • Rangeland • Reseeding • Herbicide residue • Agropyron cristatum L. Gaertn.

¹ Cooperative project of Brigham Young Univ., Provo, UT 84602 and Intermountain Res. Stn., USDA Forest Service, Ogden, UT 83702. This publication reports research involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate state and/or federal agencies before they can be recommended.

² Associate professor, Brigham Young Univ., Provo, UT and range scientist, Intermountain Res. Stn., USDA, Forest Service, Boise, ID.

Received for publication December 22, 1986.