Typically, the black spots fall out, giving the leaf a shot-hole appearance. Leaves with multiple infections turn light green, then yellow, and drop from the tree. Defoliation can reduce yields and lessen winter hardiness. Spots first appear in the spring as the new leaves approach full size. This disease is made worse by mild, wet weather.
New spots can appear through late summer.
To control leaf spot in the home orchard, try to remove all diseased leaves at the end of the season. Do not apply the chlorothalonil during harvest. Diseases of Trees and Shrubs, Cornell University Press, pg 66 2. Hort '97 Newsletter, No. 25, June 25, 1997.