The relative persistence of trifluralin (545 EC and 5 G) and ethalfluralin in prairie soils

Abstract

The persistence in soil of trifluralin 545 EC, trifluralin 5 G, and ethalfluralin 360 EC was studied over a 2-yr period at three different sites in Saskatchewan. At two of the three sites both formulations of trifluralin were more persistent than ethalfluralin when a canola crop was grown in the treated soil. In the high organic matter soil at the third site the persistence of trifluralin and ethalfluralin was similar under both fallow and cropped conditions. Crop response data gathered from wheat, oat and millet stands plus gas chromatographic analysis of soil extracts indicated that trifluralin 545 EC and trifluralin 5 G persisted in soil for comparable lengths of time when applied at rates between 0.85 and 1.40 kg a.i. ha−1. At recommended application rates to summerfallowed fields, the amount of herbicide remaining in the different soils at seeding time the following season was least for ethalfluralin 360 EC. The average amount of trifluralin 545 EC, trifluralin 5 G and ethalfluralin 360 EC which remained in the soil at the three field locations the year following application was 13, 13 and 6%, respectively. Key words: Trifluralin, ethalfluralin, herbicide persistence