Simulations of Fungicide Runoff Following Applications for Turfgrass Disease Control

Computer simulations of fungicide loading in surface water runoff were conducted with fungicides commonly used in golf course fairways and lawns in Kentucky. For all fungicides, values for degradation half-life and organic carbon partition coefficient were obtained from published sources; other input parameters were selected to simulate conditions typical in local swards. Spray programs were tested using a 21-year period of weather data for Lexington, KY. Predicted amounts of fungicide in runoff were determined, and predicted fungicide concentrations in runoff (mg/liter) were compared with 50% lethal concentration (LC₅₀) values for rainbow trout and Daphnia magna. All simulated chlorothalonil applications produced runoff with concentrations that greatly exceeded the LC₅₀ values for both indicator species. For some applications, concentrations of azoxystrobin, iprodione, and pentachloronitrobenzene exceeded LC₅₀ values of at least one indicator species. Under the conditions simulated, runoff concentrations of metalaxyl, propiconazole, thiophanate methyl, and triadimefon were well below LC₅₀ values of the indicator species. Although actual amounts of fungicide loaded into runoff were relatively low, these simulations suggest that turfgrass applications of fungicides with high intrinsic toxicity to indicator species could pose a risk to populations of primary and secondary consumers in aquatic ecosystems.