Apple scab usually appears as spots on leaves. A leaf with several spots will later turn yellow and drop. Highly susceptible varieties may lose most of their foliage by midsummer. The heavy defoliation will weaken the trees slightly, but will usually not kill them. Scab may also infect the fruit.
Infected fruit have distinct brown or black spots with irregular margins.
When severe, the skin splits open and fruit becomes irregularly shaped. Cultural methods of disease management produce better results in relatively dry years and, in some situations, may even eliminate the need for fungicides. A properly pruned open tree canopy has better air circulation which allows for faster drying of leaves and reduction of the number of infections. Because the apple scab fungus overwinters in apples and leaves on the ground, raking and removing fallen leaves and apples is recommended. Selection of high quality, disease resistant varieties is desirable since there are differences in susceptibility.