Determining the optimal ratio of resistant to susceptible bentgrass cultivars to reduce dollar spot severity

Abstract Dollar spot, caused by Clarireedia spp., is the most prevalent disease on creeping bentgrass golf fairways. Interseeding newer dollar spot‐resistant cultivars into susceptible bentgrass stands could reduce dollar spot severity and the need for resultant fungicide use. This study was conducted to determine the optimal ratio of resistant to susceptible cultivars in a blend that will result in dollar spot reduction. Greenhouse experiments were conducted on cultivar blend ratios (0%, 10%, 25%, 50%, 75%, 90%, 100%) of dollar spot‐resistant (Pure Select, 007XL, Coho) and susceptible (Penncross) bentgrass challenged with inoculation of two Clarireedia spp. isolates. Disease severity was determined using visual estimates and digital image analysis. Dollar spot severity was significantly influenced by the Clarireedia isolate, with a fungicide‐resistant isolate being more aggressive and producing more disease than a sensitive one. Dollar spot severity was highest on Penncross alone, with no statistical differences observed among the resistant cultivar monostands. Mean disease severity of the blended cultivar ratios was divided into three statistically different groups—low resistance (10% and 25%), medium resistance (50% and 75%), and high resistance (90% and 100%). Compared to Penncross, blending a 10% resistant cultivar reduced AUDPC (area under the disease progress curve) values by 2% and 3% in Experiments 1 and 2, respectively, while blending a 90% resistant cultivar yielded 20% and 32% reductions. These results indicate dollar spot severity decreases as the ratio of the resistant cultivar in a stand increases, and blending resistant cultivars into susceptible has the potential for reducing disease.