Overwintering of Alternaria mali, the Causal Agent of Alternaria Blotch of Apple. Nenad Filajdic, Former Graduate Research Assistant; North Carolina State University, Raleigh 27695 . T. B. Sutton, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Plant Dis. 79:695-698. Accepted for publication 27 February 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0695.

Survival of Alternaria mali in lesions on leaves on grass or bare ground, in lesions on terminals, and as conidia in buds of Delicious apple trees was examined in three distinct orchard environments in North Carolina. No lesions were observed on terminals. Leaves on the ground were a more important overwintering site than buds at all three locations. Mean number of conidia detected per leaf averaged over all three locations and 2 years was 66.7, whereas an average of only 2.8 conidia per bud were detected. Conidia from buds also had lower germination (6.5%) than conidia from leaves (38.8%). Number of conidia per leaf and conidial germination did not differ consistently among locations. Number of overwintering conidia detected per leaf did not decrease from November 1991 to May 1992, but was less in May 1993 than in November 1992. Treatment of leaves with urea in the fall had minimal effects on amount of leaf area remaining in May. Overwintering on grass or bare ground or treatment with urea did not affect the number of conidia detected per leaf or their ability to germinate.