Apple scab

Apple scab is caused by the fungus Venturia inaqualis which can also infect pears, mountain ash, hawthorn and cotoneaser. The scab overwinters on infected leaves that fall on the ground. By late winter or early spring, spores begin to develop. Spring rains and winds carry the spores to nearby trees and re-infect the newly emerging leaves.

• Scab may form on leaves, fruit, leaf and fruit stems, and green twigs.  Infections occur as rough circular brown to olive green lesions.  Lesions on fruit turn dark brown and black and become corky or scab-lik

• Practice good garden sanitation. The fungus can harbour in fallen leaves. Rake up leaves in fall before the snow falls. Leaves can be burned, buried or composted. Even with good sanitation, spores from neighbouring trees can return to infect the tree the following year.
• Keep trees properly pruned. An overgrown or dense canopy encourages the fungus, which needs moisture to grow. Trees with an airy, open canopy allows leaves to dry quickly, which can reduce the severity of the disease. Apple trees should be pruned in late winter or early spring before the tree leafs out. See our pruning video here: USask Fruit Tree Pruning Video
• Fungicide sprays are only potentially effective if applied when the disease is active, which is usually at the beginning of or shortly after the green tip stage of the leaf.  

Check the susceptibility of scab for different cultivars.  Cultivars that are immune to apple scab are available.