Management of dollar spot, caused by the fungus Sclerotinia homoeocarpa, is dependent upon repeated fungicide applications in intensively managed turfgrass such as golf course putting greens and fairways. Repeated fungicide applications could potentially select for fungicide-resistant isolates and result in a reduction of disease control. The objectives of this study were to determine the degree of S. homoeocarpa in vitro sensitivity to the fungicides thiophanate-methyl and propiconazole using isolates collected from golf course putting greens, fairways, and roughs; and to determine the relationships of golf course age and fungicide history to the frequency of fungicide-insensitive isolates within the population. More than 1,400 S. homoeocarpa isolates were collected from putting greens, fairways, and roughs at six Wisconsin golf courses and one Massachusetts golf course and subjected to in vitro fungicide sensitivity assays with single discriminatory concentrations of thiophanate-methyl and propiconazole. Five of seven pathogen populations from rough areas were not significantly different from one another in propiconazole sensitivity. These populations were collectively the most sensitive to both fungicides and therefore, served as baseline populations for comparison with fungicide-exposed populations from putting greens and fairways. Greater propiconazole insensitivity was observed in populations collected from fairways and putting greens that received more frequent applications of the fungicide than those isolated from the roughs. In nearly all the golf courses, the frequency of thiophanate-methyl insensitivity was higher among isolates of S. homoeocarpa collected from fairways than from roughs regardless of the age of the golf course or history of benzimidazole use. Thus, while the development of resistance to propiconazole can be predicted in part by the relative frequency of demethylation inhibitor fungicide applications, the occurrence of populations resistant to thiophanate-methyl appears to be unrelated to recent use of the benzimidazole class of fungicides.
Populations of Japanese beetle at sites in Michigan where Ovavesicula popilliae (Andreadis) was introduced in 1999 and 2000 were compared with nearby control sites from fall of 2005 through spring of 2008. Percent infection by O. popilliae and winter mortality of Japanese beetle were determined by sampling larvae in October and April from 12 golf holes on six courses in southeast Michigan and eight holes on four courses in southwest Michigan. Adult Japanese beetles were also collected from these golf courses in July and August of 2007 to determine the impact of O. popilliae-infection on egg development in females. In southeast Michigan, O. popilliae appeared to spread rapidly from the 100 m(2) plots where it was previously introduced to surrounding golf course holes between 2000 and 2006. However, data from southwest Michigan suggests that O. popilliae had already been introduced into the area. Regression analysis of data from all 20 golf course holes gives a significant relationship between percent infection of larvae with O. popilliae and winter mortality of Japanese beetle. Mean winter mortality of larvae around golf course holes where <10% were infected with O. popilliae was 24.7% compared with 41.7% mortality where 10-30% were infected, and 72.0% mortality where >30% were infected. Females infected with O. popilliae contained 50% fewer mature eggs than uninfected females. In addition, females from golf courses where all of the fairways and roughs were treated annually with imidacloprid contained 48% fewer mature eggs than females from golf courses where insecticides were only used on the fairways or not at all.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.