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Poster: Biology & Disease Mgmt: Chemical Control


Fungicide sensitivity of Monilinia vaccinii-corymbosi in highbush blueberries in Michigan
K. FITZGERALD (1), J. Gillett (1), A. Schilder (1) (1) Michigan State University, U.S.A.

Mummy berry in blueberries, caused by the fungus Monilinia vaccinii-corymbosi (Mvc), is usually controlled with fungicides, in particular sterol inhibitors which have been used for almost 20 years. Fungicide sensitivity of Mvc isolates was studied across Michigan. Isolates were collected from various field sites and grown in pure culture: 72 isolates were tested in poison agar assays using six concentrations of three commonly used fungicides in the sterol inhibitor class (fenbuconazole, metconazole, and prothioconazole). Commercial formulations of these products were used. Colony diameter was measured after an incubation of 14 days at 22 degrees C in the dark and compared to growth on non-amended PDA. EC50 values were calculated for all isolates using a four-parameter logistical curve fit in the computer program R. EC50 values ranged from 0.0016 to 0.0146 ppm for fenbuconazole, 0.0007 to 0.0104 ppm for metconazole, and 0.0021 to 0.0986 ppm for prothioconazole. A slight shift towards reduced fungicide sensitivity was detected in more intensively managed fields compared to baseline sites; however, highly resistant isolates were not detected. The ITS region of the ribosomal DNA of the isolates was sequenced to confirm their identity and assess species-level genetic diversity. All isolates were nearly identical. Allthough the risk of sterol inhibitor resistance in Mvc appears to be relatively low, fungicide resistance management is still imperative.