Numerous shot holes give a tattered appearance to leaves. Coryneum blight also will infect leaf buds, blossom buds and twigs, and cause small, sunken twig cankers. Infection to these areas weakens a tree. More serious damage shows up as blemished or disfigured fruit. Spots may appear on the fruit anywhere from 10 to 12 weeks prior to harvest and throughout the post-harvest period.
Spots are sunken, brownish and up to one-half inch in diameter.
During optimal conditions, spots will coalesce and may cause skin cracking or gumming. Optimal conditions for disease include frequent light showers combined with wind and prolonged warm weather of 70 to 80 degrees Fahrenheit. Wind isn't required but will help spread the disease as spores are picked up and moved to uninfected branches. Blight will spread rapidly within a tree, but will spread more slowly from tree to tree. Be especially alert to blight in spring and early summer.