Using ELISA to Determine the Effect of Temperature On the Degradation of the Fungicides Chlorothalonil and Iprodione On Golf Course Turfgrass.

Fungicides are the primary means for controlling most fungal diseases of intensively managed turfgrass. Repeated fungicide applications are often made based on label recommendations, with little regard to the environmental conditions present. Under warm, wet conditions that often lead to disease development it is usually recommended to shorten the fungicide reapplication interval for more effective disease control. Whether the environmental conditions increase pathogen aggressiveness, hasten fungicide degradation, or both is poorly understood. To determine the impact of temperature on fungicide degradation in the field, creeping bentgrass maintained at a height of 1.2 cm was sprayed with iprodione, chlorothalonil, or a mixture of both in the summer of 2010. One hour following the fungicide application, 5 cm diameter cores were sampled from the field and placed in growth chambers set at 10°C, 20°C, or 30°C for 0, 7, 14, or 21 days. All growth chambers were maintained with relative humidity at 75% and a 12 hr photoperiod. Fungicide concentration at each date was analyzed using commercially available enzyme-linked immunosorbent assay (ELISA) sampling kits. The fungicide concentration at which disease protection failed was determined by inoculating plants at each time point with Sclerotinia homoeocarpa, the causal agent of dollar spot. Plants were inoculated in the 20°C growth chamber and radial spread of disease symptoms were quantified. Analysis of iprodione residues showed that degradation increased as temperature increased, and that at 21 d following the application there was no detectable iprodione at 30°C, approximately 50 parts per million (ppm) at 20°C, and 100 ppm at 10°C. How fungicide concentration relates to disease development is unclear at this time. The study will be repeated in 2011 to determine the effect of temperature on chlorothalonil degradation and to confirm the current findings observed with iprodione.