Problem: Scab (Apple)
This plant disease is caused by a fungus (Venturia inaequalis). It is one of the most serious diseases of apples in areas where spring weather is mild (60° to 70°F) and wet. The fungus spends the winter in infected leaf debris on the ground. Beginning at bud-break, spores are ejected into the air when the leaf debris becomes wet. Air currents carry them to emerging leaves. If a film of water is present on the leaf, the spores germinate and infect the leaf. The infected tissues produce more spores, which in turn infect other leaf and fruit surfaces. If the fruit stays wet for 2 or 3 days at a time in late summer or early fall, spores can infect the fruit, but symptoms do not develop until the fruit has been stored, sometimes for several months.
Unless severely infected, the apples are edible. To prevent recurrence of the disease the following year, remove and destroy leaf debris and infected fruit in the fall. The following spring, spray with a fungicide labeled for edibles.