Symptoms of Apple Scab on MacIntosh Apple
Apple trees and crab apple trees are seriously infected by the Apple Scab fungus. Scab is especially serious in wet seasons when the secondary, tertiary....etc. infection cycles by conidia (Spilocaea state) cause serious spotting on the leaves with premature defoliation. The fungus also causes significant malformation and premature drop of fruits infected early in the season. The silvery border round the scab, on the fruit above, is caused by air trapped under the raised cuticle. This fungus is a subcuticular parasite and does not affect the flesh of the fruit.
In fruit trees, several applications of fungicide are necessary to effect control. Note: Apples are not a good choice for a backyard orchard in scab areas nor are crab apples as ornamentals. Heavy scab and early defoliation in wet years make the plants unsightly.