Frequent pesticide applications to golf courses causes concern that surface water may become contaminated. We hypothesized that runoff potential of these pesticides could be predicted by the recently developed Opus model. We conducted a 3-yr field study measuring surface runoff of water and dimethylamine salts of 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba (3,6-dichloro-2-methylphenoxy-benzoic acid), and mecoprop [(±)-2-(4-chloro-2-methylphenoxy)-propanoic acid]. Twelve 7.4 m by 3.7 m plots of ‘Tifway 419’ bermudagrass (Cynodon dactylon (L.) Pers.× C. transvaalensis Burtt Davy) were managed as a golf course fairway. Simulated rainfall was applied at an average intensity of 29 mm h−1 1 d before and 1,2,4, and 8 d after pesticide application for 0.92, 1.75, 1.75, 0.92, and 0.92 h, respectively. Average annual runoff loss was 9.13, 15.41, and 10.82% of applied 2,4-D, dicamba, and mecoprop, respectively. Both mass and concentration of pesticide runoff decreased rapidly, with the first posttreatment event runoff averaging 74.5, 71.7, and 73.0% of the total runoff of 2,4-D, dicamba, and mecoprop, respectively. The Opus model adequately simulated runoff [R2 = 0.897 and normalized root mean square error (NRMSE) = 24.6%]. The 2,4-D in runoff was better simulated by complete-kinetic sorption (R2 = 0.876, NRMSE = 60.2%) than by equilibrium sorption (R2 = 0.848, NRMSE = 68.2%). Opus did not accurately simulate 2,4-D over all runoff events, but simulated 2,4-D in the first posttreatment runoff within a factor of 2 of those measured.
This study was supported in part by grants from the U.S. Golf Association and the National Research Initiative Competitive Grants Program, USDA, Cooperative Research Service.