Canker diseases cause dieback of individual branches or entire trees. Prune out diseased branches, fertilize regularly, and water during dry weather. There is no chemical control.
Leaf blister caused by Taphrina virginica causes blistered or deformed leaves.
Leaf spots are generally not serious. Rake up and destroy infected leaves at the end of the growing season.
Powdery mildew makes a white coating on the leaves. Use benomyl when control is needed.