By Annette Meyer I have received several telephone calls about leaves on apple and crabapple trees turning brown and then black. The disease causing this problem is called fire blight.
Fire blight is a disease caused by a bacterium.
The bacteria enter the tree through wounds and natural openings in the leaves and bark, and by bees pollinating the flowers. Many cultivars of apple, crabapple, and pear trees are susceptible to fire blight and are injured by this disease. However, fire blight also occurs on many landscape trees and shrubs in the rose family. Fire blight infects callery pear, several species of cotoneaster and hawthorn. The fire blight bacteria overwinter in cankers formed during the infections that took place during the previous growing season.