Cover St ory
Dollar Spot:
New Approaches to Controlling an Old Disease
By David Shell, Graduate Teaching Assistant, Plant Sciences Department, The University of Tennessee
D
ollar spot, which is caused by the fungal pathogen Sclerotinia homoeocarpa, is a common disease of turfgrasses. All turfgrass species are susceptible, although some differences in susceptibility exist among species. Most diseases require free moisture to start the infection process; dollar spot, though, is unique in that it prefers drier conditions for infection. Having said that, it is important to not over-water to limit the spread of dollar spot because over-watering will cause far greater problems. When conditions are conducive for disease development, white mycelium, which will resemble cotton, will be evident in the morning (Photo 1). Chlorotic lesions with tan to reddishbrown margins will be present on individual leaves. Patches of dollar spot rarely exceed two inches, but individual patches can coalesce into bigger patches, making the disease more severe. Current management techniques include managing moisture, 20
maintaining adequate fertility (especially nitrogen) and the use of fungicides when needed. New techniques are being investigated to give turf managers better options for disease control.
Dollar spot prediction model Dr. Damon Smith, from the University of Wisconsin, and Dr. Jim Kerns, from North Carolina State University, developed a model to predict the probability that a dollar spot epidemic will occur. It uses a five-day rolling window of temperature and relative humidity or relative humidity alone. This model is adjustable so that it allows you to set different probabilities for greens, tees and fairways. We tested this model in 2011 and 2012. In 2011, we made six fungicide applications, which were two fewer applications than the other treatments in our program’s trial. The model provided significantly better control than the untreated control and per-
TENNESSEE TURFGRASS April/may 2015 Email TTA at: tnturfgrassassn@aol.com