By 1993, growers in nine counties in southern and central Virginia reported seeing this problem, some with as much as 50 to 60 percent defoliation on 'Delicious'. Although leaf blotch severity may vary from year to year, there are strong indications that it has spread to new areas in North Carolina and Virginia, and could become a problem in more northern areas of the mid-Atlantic region. Disease severity is aggravated by severe mite infestation. Maintaining good mite management is an important factor in preventing severe disease development. When lesions occur on petioles, the leaves turn yellow and 50 percent or more defoliation may occur.
Severe defoliation leads to premature fruit drop.
Alternaria leaf blotch is most likely to occur on 'Delicious' strains and should not be confused with frogeye leaf spot, captan spot, or with'Golden Delicious' necrotic leaf blotch. Frogeye leaf spot usually appears earlier in the season and is associated with nearby dead wood or fruit mummies. Golden Delicious' necrotic leaf blotch commonly occurs in July and August as a result of physiological stress caused by fluctuating soil moisture. Typically, the incidence of fruit infection is relatively low, but in heavily defoliated orchards, fruit infection as high as 60 percent has been reported. The fungus can overwinter as mycelium on dead leaves on the orchard floor, in mechanical injuries in twigs, or in dormant buds.