Info Bulletin: Apple Scab
A foliar disease that causes loss of leaves, reduction in fruit yield, and inedible fruit. Common in most types of apple trees, especially common in crab apple trees.
- Light brown or black spots on leaves
- Spotted leaves turning yellow and falling
- Fruit with distinct brown or black spots with irregular margins
- Splitting fruit skin
- Irregularly shaped fruit
Apple Scab is caused by a fungus called Venturia inaequalis. During the late spring, summer, and early fall, it continually produces spores which cause new infections. The fungus over winters in fallen leaves on the ground and in spring the spores become active again and infect the new growth on the tree. If scab is severe for several years, fruit production slows and eventually stops. Severe infections over several consecutive years can cause branches to dieback, or even trees to die. The disease is especially severe following prolonged cool, damp spring weather.
Pruning the tree to provide better air and sunlight penetration will help to allow leaves to dry faster, thereby reducing the chances of infection. Raking and destroying fallen leaves also helps by eliminating sources of infection. Finally, fungicide treatments may be necessary. Normally 3-4 applications early in spring are sufficient to control apple scab.