OVERWINTERING OF ALTERNARIA-MALI, THE CAUSAL AGENT OF ALTERNARIA BLOTCH OF APPLE

Survival of Alternaria mali in lesions on leaves on grass or bare grou nd, in lesions on terminals, and as conidia in buds of Delicious apple trees was examined in three distinct orchard environments in North Ca rolina. No lesions were observed on terminals. Leaves on the ground we re a more important overwintering site than buds at all three location s. Mean number of conidia detected per leaf averaged over all three lo cations and 2 years was 66.7, whereas an average of only 2.8 conidia p er bud were detected. Conidia from buds also had lower germination (6. 5%) than conidia from leaves (38.8%). Number of conidia per leaf and c onidial germination did not differ consistently among locations. Numbe r of overwintering conidia detected per leaf did not decrease from Nov ember 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 amo unt of leaf area remaining in May. Overwintering on grass or bare grou nd or treatment with urea did not affect the number of conidia detecte d per leaf or their ability to germinate.