Coastal bermudagrass and forage corn were treated with Dasanit®, O, O-diethyl O-[P-(methylsulfinyl) phenyl] phosphorothioate, EC at 0.5, 1.0, and 2.0 lb/AI acre and sampled 0, 1, 7, 14, 21, and 28 days posttreatment. Quartsize glass-jar corn silage was made from the 1-day posttreatment sampling. Residue analyses showed a gradual oxidation in the field to the 3 metabolites (mostly P = S, SO2 and P = O, SO2)' After 28 days of weathering, total residues remaining in grass and corn treated at the highest level (5.96 and 2.80 in. of rainfall, respectively) were about 4 and 7 ppm (wet basis), respectively. In the corn-silage tests, the residues were essentially stable during a 30-day aging period held at 85°F.