DISSIPATION OF GLYPHOSATE AND ITS METABOLITE AMPA IN ESTABLISHED CRESTED WHEATGRASS FOLLOWING SPRING APPLICATION

Using glyphosate to suppress resident vegetation while establishing sod-seeded alfalfa in pastures may result in unacceptably high residues within the treated foliage. In a 2-yr study, the dissipation of glyphosate and its major metabolite, AMPA, was measured in the foliage of established crested wheatgrass [Agropyron desertorum (Fisch.) Schult.] following spring application at 2.2 kg a.i. ha(-1). Within 2 wk, glyphosate residues had decreased to <50 mg kg(-1), the international MRL for fodder of grasses. Washoff by rainfall appeared to be the major route of dissipation. Residues of AMPA were generally about one order of magnitude less than the corresponding glyphosate residues.