Factors affecting pesticide runoff from warm-season turfgrasses
Ampim, Peter Agbeehia Yao
CommitteeRankins Jr., Alfred
Knowledge of the impacts of management and scale are important for improved understanding and prediction of turf chemical runoff in urban environments. This study addressed the effects of mowing height, warm-season turf species and plot size on runoff of water, bromide, dimethylamine salts of the herbicides 2, 4-D, MCPP and dicamba, flutolanil fungicide, and chlorpyrifos insecticide from a Brooksville silty clay soil. The runoff plots were sloped at 3 % and arranged as split-plot in a randomized complete block design. The pesticides were applied as a tank mix: 2, 4-D at 1.12 kg ai/ha, MCPP at 1.80 kg ai/ha, dicamba at 0.50 kg ai/ha, flutolanil at 2.24 kg ai/ha and chlorpyrifos at 2.24 kg ai/ha. Bromide was applied separately at 15 kg ai/ha. The pesticides and bromide were applied 24 h and 0.5 h respectively, prior to each rainfall simulation event. Rainfall simulated at 38 mm/h was applied to treated plots for 1.5 h to generate runoff which was collected at 5 minute intervals. Pesticide runoff concentrations were determined by reverse-phase HPLC using UV-Vis detection. The limit of quantification for each compound was approximately 5 µg/L. Bromide was analyzed for by an ion selective electrode following EPA method 9211 with the limit of detection at 200µg/L. Plot size, mowing height and/or grass species significantly affected different runoff aspects of the pesticides investigated at p< 0.05. Averaged across treatments, percentages of applied pesticide lost in runoff were 43.3 ± 12.7 for 2, 4-D, 29.5 ± 8.3 for MCPP, 24.6 ± 8.3 for dicamba, 6.8 ± 1.0 for flutolanil and 0.22 ± 0.04 for chlorpyrifos. Similarly, average peak pesticide concentrations were 3.7 ± 0.9 mg/L for 2, 4-D, 4.2 ± 1.1 mg/L for MCPP, 1.2 ± 0.3 mg/L for dicamba, 0.8 ± 0.3 mg/L for flutolanil and 0.04 ± 0.02 mg/L for chlorpyrifos. Results obtained for water and bromide runoff suggest that the treatment effects observed for the pesticides were due to differences in retention mechanism rather than turf hydrology. Linear relationships were obtained between plot area and chemical mass and total runoff indicating that runoff from bermudagrass turf is ‘scalable’.