In Vitro Activity of Etaconazole, Bitertanol, and Fenarimol on Fungi Causing Summer Diseases of Apples. T. B. Sutton, Department of Plant Pathology, North Carolina State University, Raleigh 27695. J. F. Nardacci, and A. L. O’leary, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Plant Dis. 69:700-703. Accepted for publication 25 February 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-700.

The in vitro sensitivity, as measured by radial growth inhibition, of Botryosphaeria dothidea, Physalospora obtusa, Glomerella cingulata, Colletotrichum gloeosporioides, Helminthosporium papulosum, Mycosphaerella pomi, Gloeodes pomigena, and Zygophiala jamaicensis to etaconazole, bitertanol, and fenarimol was determined. Except for G. pomigena, EC₅₀ values were less than 10 μg a.i./ml for each fungus-fungicide combination. Fenarimol was generally the least active of the compounds tested. Isolates of each fungus varied in their sensitivity to the compounds, indicating the potential for the selection of less sensitive strains under orchard conditions. Poor control of the summer diseases in the orchard by sterol-inhibiting fungicides may be due to their lack of persistence or to poor uptake of the compounds by fruit.