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. Michigan Golf Course Superintendents Association | WWW.MiGCSA.ORG
From The Campus
Rolling, Resistance, Reduction: A Dollar Spot Management Strategy BY RYAN BEARSS, NANCY DYKEMA, DR. JOE VARGAS MICHIGAN STATE UNIVERSITY
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early one century since its discovery, and we are still searching for better ways to mitigate the problem that is dollar spot disease of turfgrass. The Voldemort of the turfgrass industry, superintendents cringe upon hearing its very name and spring into action at the site of those tiny spots. With a single fungicide application ranging from $1000-$6000 in product alone (given 25 acres of fairway), dollar spot stresses golf course budgets and, according to Dr. Joe Vargas, is the most economically significant disease in the golf course industry today. A foliar disease caused by the pathogen Rutstroemia floccosum syn. Sclerotinia homoeocarpa, dollar spot is active from May-September in Michigan, disseminating by the spread of infected clippings such as on golf spikes, mowers, and other turf equipment. When humidity is high, temperatures are high (60-90°F) and nighttime temperatures are cool, the dormant fungus germinates producing mycelia, the fluffy white material that bares resemblance to spider webs. Small, bleached, hourglassshaped lesions can be observed on individual blades of grass. Susceptibility for infection increases under stressful conditions such as low fertility and drought. As the fungal mycelia spread and the disease epidemic builds, small, silver dollar-sized depressed spots are formed in the turf. In a
cluster, these small spots form sunken areas that eventually coalesce creating larger areas of necrosis leaving an uneven playing surface for golfers. In addition to cost and effect on playability, several additional variables of this disease make management of dollar spot for superintendents very difficult: • Fungicide resistance. Resistance of the fungal pathogen to many different classes of fungicides exist. • Multiple fungicide applications throughout the growing season are typically required to manage the disease. • Public demand for reduction in pesticide use. • The less-is-more mindset. Superintendents often starve their greens for increased greens speed. Low nitrogen=increased stress=increased susceptibility to dollar spot. • Low height of cut. Mowing is a stressful practice for turf but necessary to maintain a playable surface. Again increased stress leads to increased susceptibility to dollar spot. • Reduction of irrigation. By choice or by law, reduction of irrigation increases greens speed but produces a less vigorous plant. • Timing. Contact fungicides are typically less expensive than systemic fungicides but must be applied preventively and more frequently for maximum efficacy.