Effect of Adjuvant on S-Metolachlor and Fluometuron Sorption to Soil and Efficacy

Abstract

Residual weed control is influenced by herbicide-soil interactions. This study was conducted to determine whether herbicide sorption to soils and subsequent residual weed control can be manipulated with adjuvants included in tank mixtures. The effects of commercially available adjuvants on S-metolachlor and fluometuron sorption in the laboratory and residual control of barnyardgrass with these herbicides under field conditions were investigated on a Mantachie loam, Catalpa silty clay loam, and Marietta fine sandy loam. The addition of an adjuvant never increased herbicide sorption to soil but, rather, had no effect or decreased the sorption of S-metolachlor and fluometuron. In all tested soil types, sorption of S-metolachlor decreased by up to 17.6-fold. In silty clay loam and loam soil types, the adjuvant did not affect fluometuron sorption. However, in fine sandy loam soils, two of four experimented adjuvants decreased sorption of fluometuron to soil particles up to 1.6-fold. Moreover, no adjuvant influenced the residual control of barnyardgrass exhibited by either chemistry. These data indicate that the addition of an adjuvant to S-metolachlor and fluometuron mixtures will not increase their sorption to loam, silty clay loam, or fine sandy loam soils or alter the efficacy of these herbicides under field conditions.