Field evaluations and in vitro sensitivity of Microdochium nivale to succinate dehydrogenase (SDHI) fungicides
2022
Hockemeyer, Kurt | Koch, Paul L.
Microdochium patch is a destructive disease of amenity turfgrass caused by the fungus Microdochium nivale (Fries) Samuels & I.C. Hallett. The succinate dehydrogenase (SDHI) class of fungicides is a relatively new class and their efficacy against M. nivale remains unclear. Fluxapyroxad (3‐(difluoromethyl)‐1‐methyl‐N‐[2‐(3,4,5‐trifluorophenyl)phenyl]pyrazole‐4‐carboxamide), penthiopyrad (1‐methyl‐N‐[2‐(4‐methylpentan‐2‐yl)thiophen‐3‐yl]‐3‐(trifluoromethyl)pyrazole‐4‐carboxamide), and pydiflumetofen (3‐(difluoromethyl)‐N‐methoxy‐1‐methyl‐N‐[(2R)‐1‐(2,4,6‐trichlorophenyl)propan‐2‐yl]pyrazole‐4‐carboxamide) were evaluated for their field and in vitro efficacy against M. nivale during the winter of 2019–2020 in Madison, WI. The field plots were inoculated with M. nivale following treatment application to encourage fungal infection. The in vitro efficacy of each compound against M. nivale was conducted by determining radial growth inhibition on potato dextrose agar at two different temperatures (10 and 20 °C). In the field study, disease pressure was high and none of the fungicides reduced disease severity relative to the non‐treated control, including the positive control fungicide treatment. For the in vitro study, pydiflumetofen consistently reduced relative colony growth the most regardless of incubation temperature and penthiopyrad was the least potent. This research indicates that certain SDHI fungicides are highly potent against M. nivale in vitro, but additional factors such as environmental degradation and/or variable fungal uptake may decrease their efficacy in the field.
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