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Infection of Grape by Guignardia bidwellii—Factors Affecting Lesion Development, Conidial Dispersal, and Conidial Populations on Leaves. R. A. Spotts, Former assistant professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster, 44691 and The Ohio State University, Columbus 43210, Present address: Oregon State University, Mid-Columbia Experiment Station, 3005 Experiment Station Drive, Hood River, 97031; Phytopathology 70:252-255. Accepted for publication 10 September 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-252.

Experiments were conducted to evaluate the effects of temperature and relative humidity on incubation time and pycnidia formation of Guignardia bidwellii on grape leaves and to study factors affecting conidial release and adherence to and populations on leaf surfaces. Incubation time was approximately 1 wk at 21 and 26.5 C and 2 wk at 15 C. After lesions appeared, pycnidia formed within 3 (21 C) to 5.5 (15 C) days. Rainfall duration of 1–3 hr provided optimal conidia dispersal. Conidia were readily washed from inoculated leaves except when they were dry for 60 min or longer preceding washing. Conidial populations on leaves in the vineyard were closely related to conditions favoring conidial dispersal, retention on leaves, and disease severity.

Additional keywords: epidemiology, Vitis spp., grape black rot.