Apple scab is the most common disease that affects crabapple trees. The fungus venturia inaequalis causes apple scab, which appears as velvet-like brown or black spots on crabapple leaves. In severe cases, the crabapple tree will lose all of its' leaves by mid-summer.
About this Author
Amy Deemer began her writing career in 1992. She began writing online content in 2009 and writes primarily for Answerbag and Garden Guides. Deemer enjoys researching and writing about flowers, plants and gardening. Deemer has an Associate of Arts in liberal studies from Westmoreland Community College.