Cankers in apple trees can be caused by more than a dozen different pathogens. In New York, however, the most common canker pathogens are Erwinia amylovora, the cause of fire blight, Botryosphaeria obtusa, the cause of black rot canker, and Botryosphaeria dothidea, the cause of white rot canker. E. amylovora is unique among apple canker pathogens because it is a bacterium, whereas fungi cause most of the other cankers on apples. Also, E. amylovora can invade and kill healthy trees, whereas most of the fungi causing apple cankers are relatively weak pathogens that appear primarily in stressed trees.
Fungal cankers usually appear in apple trees only after trees have been predisposed to infection by adverse weather conditions, wounding, inappropriate horticultural practices, or presence of other pathogens in the older wood in the tree. Studying canker diseases in apples is difficult because of the numerous interactions that contribute to canker development. For more information, see the following 2007 article in New York Fruit Quarterly:
2007 Canker Problems in Apple Orchards
Updated 28 Dec. 2017
