Lesions may appear more numerous closer to the mid-vein of the leaf. If heavily infected, the leaf becomes distorted and drops early in the summer. Trees of highly susceptible varieties may be severely defoliated by mid to late summer. Fruit symptoms are similar to those found on leaves. The margins of the spots, however, are more distinct on the fruit.
Scabs are unsightly, but are only skin deep.
Badly scabbed fruit becomes deformed and may fall before reaching good size. Causal Organism Apple scab is caused by the fungus, Venturia inaequalis . It survives the winter in the previous year's diseased leaves that have fallen under the tree. In the spring, the fungus in old diseased leaves produces millions of spores. These spores are released into the air during rain periods in April, May and June.