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’.

There have been many changes in production agriculture over the last 20 years. The use of herbicide resistant crops has become common place in production agriculture. However, the release of crops resistant to auxin herbicides has brought more attention to the pesticide application process regardless of the type of pesticide applied. Moreover, controlling off-target movement of pesticides has become an integral part of the day to day farming tasks. The use of deposition aids when applied with water has been documented; however, the effect of deposition aids on pesticide application is not well understood. Based on these findings, selecting a deposition aid not only can be affected by the pesticide used but also the crop in question. Additionally, label restrictions on auxin herbicide application in auxin tolerant crops brings an additional problem to cotton growers. The use of insecticides in conjuction with herbicide applications has been commonplace for many growers across the cotton belt. However, smaller droplets have been utilized to increase coverage of these insecticides. Data presented in these findings suggest that larger droplets can still have good levels of efficacy and in some instances increase yield. The use of auxin tolerant crops allows for usage of addition POST herbicides to cotton; however, the effect of these tank mix applications on ctrop injury is not well understood. In both EnlistTM and Xtend® Flex cotton levels of injury were increased when glufosinate and S-metolachlor were applied in a tank mix. However, yield was not negatively impacted in either study.

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