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Factors Affecting Apple Leaf Scar Infection by Nectria galligena Conidia. H. J. Dubin, Research Assistant, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Botany and Plant Pathology, University of Maine, Orono 04473; Harley English, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 64:1201-1203. Accepted for publication 15 April 1974. DOI: 10.1094/Phyto-64-1201.

Five percent of the leaf scars of Red Delicious, Golden Delicious, and Rome Beauty apples were still susceptible to conidial infection 10 days after leaf abscission. Red Delicious was the most susceptible 1 day after leaf fall. A minimum of 6 h of free water was needed to infect Gravenstein with conidia, and increased infection occurred with longer moisture periods. Five conidia were insufficient to infect a leaf scar of Red Delicious but 50 to 5,000 conidia did so. Infection percentage increased directly with spore dose.