Tebuthiuron Distribution in Soil following Application of Pellets

Abstract

AbstractPersistence, 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 = bXa, where Y is the tebuthiuron concentration in milligrams per kilogram, b is 7.05 × 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.