Seasonal Development of Dollar Spot Epidemics in Six Creeping Bentgrass Cultivars in Maryland

Abstract

This 3-year field study evaluated the incidence and severity of dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in six creeping bentgrass (Agrostis stolonifera L.) cultivars maintained as a golf course fairway. Comparison of area under the disease progress curve (AUDPC) data clearly indicted two resistance groups among the six cultivars. ‘Crenshaw’ and ‘Backspin’ were classified as highly susceptible (HS) and the other four cultivars (i.e., ‘Penncross’, ‘Providence’, ‘L-93’, and ‘007’) were classified as moderately susceptible (MS) to dollar spot. In all three study years, there were three epidemics that began in May. Data could not be collected in HS cultivars after the first epidemic in each year as a result of severe damage. In MS cultivars, the first epidemic ended and a second began between early July and late August. The second epidemic ended approximately mid-October and a third epidemic appeared in MS cultivars between late October and early December. The second epidemic was longest and most severe, and the third fall epidemic was least severe and of shortest duration. The first epidemic in HS cultivars developed up to two weeks earlier and progressed more rapidly and severely than in MS cultivars. A growing degree-day (GDD) model, using a base air temperature of 15 °C and a start date of 1 Apr., was accurate in predicting the onset of the first epidemic in HS (60 to 70 GDD) and MS (105 to 115 GDD) cultivars during each of the three study years. Growing degree-day models are greatly influenced by the many microclimates found on golf courses and need to be evaluated for accuracy in diverse environments.