Both fungal diseases cause black or dark scabby marks to appear on the skin of the fruit, and discolouration and marks on the leaves. The fruit is still edible, although it doesn’t look very appealing or appetising. Because the fruit can crack, other diseases can get into these cracks and cause the fruit to rot.
When they cause blistering and cracking of young shoots and stems, these can provide entry points for other diseases, such as apple canker.
Both diseases are most common during a wet spring, but can appear whenever conditions are correct for the disease to develop. Scab marks can appear on the leaves at any time in spring and summer.
Apple scab and pear scab are two separate diseases, caused by very similar fungi, which affect one or the other. Apple scab cannot infect pear trees and vice versa.
Apple scab can also affect ornamental crab apples, Cotoneaster, Pyracantha and Sorbus. Pear scab can also affect ornamental pears.