Bacterial crown gall causes warty growths on the lower stems near the soil line. There is no chemical control. Destroy infected plants and avoid replanting in infected soil.
Fire blight causes the tips of the branches to die. Blighted leaves have a scorched appearance and hang on the twigs. There is no satisfactory chemical control. Prune off infected branches.
Leaf spots caused by fungi in the genera Fabraea and Cercospora may result in leaf drop when the infection is severe. A disease caused by Fabrea maculata is also called leaf blight. A fruit spot caused by Mycosphaerella pomi can cause leaf blotch. The leaf spots can be controlled with sprays of copper fungicide.