Thiophanate-Methyl and Propiconazole Sensitivity in Sclerotinia homoeocarpa Populations from Golf Courses in Wisconsin and Massachusetts

Abstract

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.

Rapid Development of Fungicide Resistance by Sclerotinia homoeocarpa on Turfgrass

“…The current study shows that S. homoeocarpa populations on turfgrass shift fast toward resistance to systemic fungicides, which may explain prevalent distribution of fungicide resistant S. homoeocarpa on golf courses in Ohio (13) and Wisconsin (14). This result also indicates that the S. homoeocarpa field populations continuously change and adapt to varying environmental conditions.…”

“…3B, WI-Green) at the O. J. Noer field in 2006. In another survey study of S. homoeocarpa fungicide resistance on six golf courses in Wisconsin and one golf course in Massachusetts, in vitro sensitivities for thiophanatemethyl and propiconazole were significantly different among the fairway, putting green, and rough within the same golf course (14). However, direct evidence of how specific factors of management practices can affect fungicide sensitivity of S. homoeocarpa populations has not been examined experimentally and remains in need of further research.…”

Characterization and distribution of mating-type genes of the turfgrass pathogen Sclerotinia homoeocarpa on a global scale

“…Management of dollar spot is becoming increasingly challenging partly due to the widespread development of fungicide-insensitive S. homoeocarpa populations (Jo et al, 2006;Koch et al, 2009;Putman et al, 2010). Contemporary isolates typically obtained from C3 or C4 photosynthetic grass hosts represent distinct evolutionary entities (Liberti et al, 2012;Taylor et al, 2009), which are referred to as the 'common (C)' and 'Floridian (F)' biotypes in Liberti et al (2012) but which we term C3 or C4 host type isolates, respectively.…”

Baseline sensitivity of Brazilian Mycosphaerella fijiensis isolates to protectant and systemic fungicides

“…Resistance to thiophanate-methyl has been reported for a number of foliar fungal plant pathogens (Luo et al, 2007;Koch et al, 2009;May-De Mio et al, 2011). However, all M. fijiensis isolates tested in this study were sensitive to this fungicide.…”