When cover sprays are stopped too soon, or when trees are not well-pruned and sprayed, severe losses can occur. Varieties such as Rome Beauty, Stayman, Jonathan, and Grimes Golden are quite susceptible.
Spots on fruit are about ¼ inch in diameter. They are somewhat irregular in shape, slightly sunken, and usually most numerous on the calyx end. On red fruit surfaces spots are red to black; on green and yellow fruit surfaces they are dark green.
Spots may be quite inconspicuous at harvest. Unless infected fruit is placed in cold storage immediately after harvest, the spots increase in size and become more sunken, thus more visible.
The disease cycle is much like that of apple scab, except it begins later in the spring. About the time of petal fall, ascospores are discharged from fallen leaves. Just how the fungus gets on the leaves is not known, as there is no evidence of the disease on leaves while they remain on the trees. Rain and high humidity favor spore discharge and infection of fruit. Infections continue until midsummer, although they decrease as the season progresses.
Routine fungicide applications normally control this disease in Pennsylvania. Summer fungicide applications should not be extended beyond 14-day intervals.