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Disease Control and Pest Management

Reduced Sensitivity to Sterol-Inhibiting Fungicides in Field Isolates of Venturia inaequalis. V. F. Stanis, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824; A. L. Jones, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. Phytopathology 75:1098-1101. Accepted for publication 6 May 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-1098.

For eight sterol-inhibiting fungicides, minimal inhibitory concentrations for preventing colony formation by individual conidia were four to eight times higher for isolates of Venturia inaequalis from one West German orchard than for isolates from either a second West German orchard or orchards in the United States. Reduced sensitivity was exhibited to BAS 454 06 F (1-(2,4-dichlorophenyl)-2-(1 H-1,2,4-triazol-1-y1)), bitertanol, CGA 71818 (1-[2-(2,4-dichlorophenyl)-pentyl]-1 H-1,2,4-triazole), DPX H6573 (bis(4-fluorophenyl)methyl(1 H-l,2,4-triazol-1-yl methyl)silane), etaconazole, fenarimol, Ro 15-1297 (1-(2,4-dichlorophenyl)-2-(3-pyridinyl)-ethanone O-methyloxime), and triflumizole. Isolates with reduced sensitivity to sterol inhibitors did not show increased sensitivity to dodine. Genetic analysis of nine isolates with reduced sensitivity indicated that reduced sensitivity was determined by a single gene.