The symptoms may be limited to small areas of the leaf or may involve the entire leaf. Infected leaves turn gray and eventually wither and fall from the tree. The disease may also occur on the fruit, blossoms, and young twigs. Infected shoots appear stunted, swollen, and chlorotic. Diseased fruits exhibit raised, wrinkled areas and often fall prematurely.
Infection occurs during the spring from bud swell to bud opening.
Spores of the fungus, which overwinter on bark and bud scales, wash onto the young leaf tissue in wet weather and initiate infections. Leaf curl is most severe when weather is wet and cool. Once the current year's leaves become infected, they cannot be treated effectively. Prepared by Paula Flynn , Department of Plant Pathology Iowa State University , Ames, Iowa. This information subject to a usage policy .