Measurement and modeling of diclosulam runoff under the influence of simulated severe rainfall

A runoff study was conducted near Tifton, GA to measure the losses of water , sediment, and diclosulam (N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro-[1,2,3 ]triazolo-[1,5c]-pyrimidine-2-sulfonamide), a new broadleaf herbicide, unde r a 50-mm-in-3-h simulated rainfall event on three separate 0.05-ha plots. Results of a runoff study were used to validate the Pesticide Root Zone Mod el (PRZM, v. 3.12) using field-measured soil, chemical, and weather inputs. The model-predicted edge-of-field diclosulam loading was within 1% of the average observed diclosulam runoff from the field study; however, partition ing between phases was not as well predicted. The model was subsequently us ed with worst-case agricultural practice inputs and a 41-yr weather record from Dublin, GA to simulate edge-of-field runoff losses for the two most pr evalent soils (Tifton and Bibb) in the south-eastern U.S. peanut (Arachis h ypogaea L.) market for 328 simulation years, and showed that the 90th perce ntile runoff amounts, expressed as percent of applied diclosulam, were 1.8, 0.6, and 5.2% for the runoff study plots and Tifton and Bibb soils, respec tively. The runoff study and modeling indicated that more than 97% of the t otal diclosulam runoff was transported off the field by water, with <3% ass ociated with the sediment. Diclosulam losses due to runoff can be further r educed by lower application rates, tillage and crop residue management prac tices that reduce edge-of-field runoff, and conservation practices such as vegetated tilter strips.