In Vitro Fungicide Sensitivity of Selected Snow Mould Isolates Collected From Amenity Turfgrasses in the United States and Norway

ABSTRACT

Snow mould diseases caused by Microdochium nivale and Typhula spp. present significant challenges to the management of turfgrass in areas with extended snow cover. Although fungicide applications are the primary control method, repeated use over decades has raised concerns about the emergence of fungicide resistance. This study evaluated the in vitro sensitivity of 12  M. nivale isolates and nine Typhula isolates ( T. incarnata and T. ishikariensis ) from selected locations in the United States and Norway to three fungicides commonly used for snow mould control: iprodione (dicarboximide), propiconazole (DMI) and azoxystrobin (QoI). Sensitivity was measured using agar‐based dose–response assays to determine the effective dose for 50% growth inhibition (EC ₅₀ ) together with species sensitivity distribution (SSD) thresholds and growth response at discriminatory concentrations (DCs). Two M. nivale isolates showed comparatively reduced sensitivity (RS): one from Wisconsin (TR1) to iprodione and one from Oregon (AG40) to azoxystrobin. Because salicylhydroxamic acid (SHAM) was not included in the azoxystrobin assay, the AG40 response should be considered preliminary rather than absolute confirmation of QoI resistance. None of the nine Typhula isolates evaluated showed clear evidence of RS under the assay conditions used. Overall, these results provide a preliminary characterisation of fungicide sensitivity among selected snow mould isolates and show that high in vitro sensitivity can persist in isolates from intensively managed sites, while some individual isolates can show RS. Expanding the sample size will be necessary to make inferences regarding the prevalence and geographic distribution of fungicide sensitivity in the snow mould populations.