VARIATION AMONG CREEPING BENTGRASS CULTIVARS IN RECOVERY FROM EPIDEMICS OF DOLLAR-SPOT

Dollar spot was allowed to develop from natural inoculum in 15 cultiva rs of creeping bentgrass (Agrostis palustris) until epidemics were wel l established. At that time, initial disease intensities were assessed , and one-half of each plot was treated with cyproconazole at 0.3 kg a .i./ha. For each cultivar, disease intensities were assessed 6 to 14 d ays after treatment in both treated and untreated subplots. Three gene ral patterns of recovery were observed: (i) significant recovery only with fungicide treatment; (ii) some recovery without treatment but gre ater recovery with treatment; and (iii) equal recovery with or without treatment. Only one cultivar exhibited the same recovery pattern in a ll 3 years; 10 of 15 cultivars exhibited the same pattern in 2 years o f testing. In 1991 and 1993, nearly all cultivars tested recovered mor e quickly when treated with cyproconazole than when left untreated. In contrast, nearly half of the cultivars in 1992 exhibited the same lev el of recovery in both treated and untreated subplots. Weather conditi ons during the 1992 test period were cooler and wetter than during the other years of the study, which probably favored host growth and turf grass recovery. While some cultivars exhibited partial resistance to d ollar spot, no consistent association was found among creeping bentgra ss cultivars between the level of partial resistance to, and recuperat ive ability from, dollar spot. Although the recuperative potential of cultivars varies in different environments, the ability to recover qui ckly from a disease outbreak could be a valuable cultivar attribute, p articularly if it can sometimes occur without a curative fungicide app lication.