114-130_Feb08 Techwell.indd

Fungicide resistance in dollar spot caused by Sclerotinia homoeocarpa is a common problem on golf courses in North America (Figure 1) (2), and managing fungicide resistance is a complex and controversial topic (1,4). With dollar spot, the question of whether to use the same fungicide until resistance develops or to rotate different chemistries and tank mixtures has not been defi nitively answered. Will the addition of contact fungicides in rotations and in tank mixtures with systemic fungicides prevent fungicide resistance? How many times can a single fungicide be used before effi cacy is reduced or complete failure occurs? Do application intervals, application timings or fungicide rates affect the development of fungicide resistance? Fungicide resistance in dollar spot is poorly understood at the population level. In sociology and biology, a population is a collection of individuals of a particular species. Individual isolates in the population may vary in genetic makeup, fungicide sensitivity, pathogenicity and vegetative compatibility. (Vegetative compatibility in fungi occurs when hyphae of two individual isolates fuse.) Our lab has attempted to carefully tease out the answers to these questions about dollar spot fungicide resistance at the population level by using DNA fi ngerprinting techniques and in-vitro assays for both fungicide sensitivity and vegetative compatibility. Our Geunhwa Jung, Ph.D. Young-Ki Jo, Ph.D. Figure 1. Dollar spot on a creeping bentgrass fairway. Photo courtesy of S. Abler