When sprays are stopped too soon, or when trees are not well-pruned and sprayed, severe losses can occur. Varieties such as Grimes Golden, Jonathan, Rome Beauty, and Stayman are quite susceptible.
Brooks spot appears on immature fruit in late June and July. Spots on fruit are about 1/4 inch in diameter, irregular in shape, slightly sunken, and usually most numerous on the calyx end. On red-skinned varieties, lesions are dark red to purple. On light-skinned varieties, lesions remain dark green. Unless infected fruit is placed in cold storage immediately after harvest, the spots increase in size and become more sunken, thus more visible.
The fungus overwinters in apple leaves on the orchard floor. About the time of petal fall, ascospores are discharged from fallen leaves. How the fungus gets on the leaves is not known since 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. Golden Delicious, Jonathan, Rome Beauty, and Stayman, are susceptible. Delicious is somewhat resistant.