Frequency of Benzimidazole- and Dicarboximide-Resistant Strains of Botrytis cinerea in Western Oregon Small Fruit and Snap Bean Plantings. K. B. JOHNSON, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. T. L. SAWYER, and M. L. POWELSON, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Plant Dis. 78:572-577. Accepted for publication 22 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0572.

In 1990 and 1991, a total of .1,496 isolates of Bolrytis cinerea were collected from strawberry, wine grape, raspberry, and snap bean plantings and from nonmanaged wild blackberry hedges located in Oregon's Willamette Valley. The percentage of isolates resistant to benomyl (5 ?g/ ml) and to vinclozolin (10 μg/ml) averaged 52 and 17%, respectively; 16% were resistant to both fungicides. The frequencies of resistance to benomyl and vinclozolin were significantly higher (P ≤ 0.05) in B. cinerea isolates obtained from strawberry than in isolates from the other crops. Of isolates of B. cinerea obtained from nonsprayed wild blackberry hedges, 38 and 6% were resistant to benomyl and vinclozolin, respectively. The frequency of benomyl-and vinclozolin-resistant strains of B. cinerea in a planting was significantly correlated (P < 0.05) with the number of applications in each respective fungicide class. Vinclozolin resistance was estimated to increase by 20.8% per fungicide application in strawberry compared with 6.4% per application in wine grape, raspberry, and snap beans. In eight strawberry fields, frequency of vinclozolin resistance declined from an average of 74% at harvest in June to 32% the following February or April. Strawberry fruit mummies harbored a higher frequency of dicarboximide-resistant strains than did leaves.

Keyword(s): gray mold