Evaluation of Fungicides for Control of Rapid Blight of Poa trivialis in Fall 2005

Rapid blight is a new disease of cool season turf grasses that has occurred on over a dozen golf courses in Arizona. It is caused by Labyrinthula terrestris, an organism in a group referred to as the marine slime molds. A trial was conducted in fall 2005-winter 2006 to evaluate efficacy of selected fungicides for control of rapid blight at a golf course in central Arizona with a previous history of disease and high salinity irrigation water (about 5 dS/m). Plots were established in late October 2005 on a practice tee on which Bermuda was overseeded with Poa trivialis. Treatments included Insignia and Fore, alone and in combinations; elemental sulfur, potassium sulfate and potassium chloride as pre-plant applications on Bermuda; gypsum, Daconil Zn, Heritage TL, Soil Life and Soil Builder. Disease symptoms appeared immediately after the first mowing. Disease ratings at 3 weeks after first mow showed that applications of the high rate of Insignia at first mow and the pre-overseed application of sulfur gave excellent control. Moderate control was shown in applications with early applications of Fore alternated with the lower rate of Insignia, Fore alone, Soil Life, and of the high rate of Insignia combined with Fore applied as a curative at first disease. Treatments with Daconil Zn, Heritage TL, Soil Builder, and preoverseed treatments with potassium sulfate, potassium chloride and gypsum gave little or no control compared to the untreated control. At 10 weeks after first mow, treatments with Insignia and the high rate of sulfur were still effective but all other treatments were either marginal or not different from the untreated control. Results show that applications of Insignia at first mow are effective for severe early season disease, and extended intervals of Insignia applications give effective long term control. Results also show that treatments of Bermudagrass with elemental sulfur reduced disease dramatically indicating that preventive chemical applications before overseeding may be possible