Evaluating SDHI Fungicide Insensitivities in Sclerotinia homoeocarpa
Allison Anthony: Department of Entomology and Plant Pathology, North Carolina State University
<div>Dollar spot is a disease of turfgrass caused by the fungus <em>Sclerotinia homoeocarpa </em>and is considered the most economically important disease of amenity turfgrass. Succinate dehydrogenase inhibitors (SDHIs) make up a group of fungicides with a growing list of products registered for turf and ornamentals, but resistance and cross-resistance within the class have been reported in some fungal pathogens. In a 2016 fungicide trial in Raleigh, NC, three SDHIs (boscalid, penthiopyrad, and fluxapyroxad) failed to control dollar spot. Twenty-four isolates were collected from dollar spot foci in the SDHI-treated and non-treated plots. A fungicide amended media assay was attempted with full-strength and ¼-strength potato dextrose agar, both including two runs of each SDHI at six concentrations (0, 0.01, 0.1, 1, 10, 100 mg fungicide/L). A plug of each isolate was placed in the center of amended media plates and radial growth was measured after 40 hours. An <em>in vivo</em> experiment was performed in which plugs of creeping bentgrass were greenhouse grown to maturity and sprayed with SDHIs at field application rates. Plants were inoculated via rye grain infested with isolates used in plate assays and kept in a growth chamber with enhanced disease conditions. Disease severity and turf quality ratings were taken every 3 days for 21 days. Results of these experiments suggest alternative plate assay methods will be needed to capture reduced sensitivity displayed by isolates <em>in vivo</em>.</div>
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