The disease can also infect crab apple and mountain-ash. Scab diseases similar to apple scab occur on pear, firethorn, and hawthorn. The scab-like leaf spots and fruit spots, from which the name was developed, may cause defoliation and reduction in fruit quantity and quality. The disease may infect leaves, petioles, pedicels, fruit and twigs. The spots are most noticeable on leaves and fruit.
Infections first appear as olive-green spots with indefinite borders.
With age, these spots become more prominent and darken to a greenish-black with a velvety appearance. Severe spotting will cause leaves to senesce and fall off. Spots on young fruit result in deformation and cracking. If infection is severe, fruit may drop off before ripening. Defoliation may result in a reduction of flower bud formation so that bloom or fruit yield the next year will be reduced.