Although plucking fresh apples from a crabapple tree is ideal, there are a few diseases that can affect the fruit and keep it from becoming edible.
Crabapple trees may become afflicted with the following diseases: apple rust, apple scab, fire blight, powdery mildew, leaf tatter, sooty mould and micronutrient chlorosis.
Apple rust can be identified by orange spots on the leaves, while apple scab is characterised by soft, olive-green specs. Shrivelled, blackened flowers and twigs are symptoms of fire blight, while leaf tatter is marked by holes in leaves. Discolouration is a symptom of micronutrient chlorosis, and a fuzzy appearance of leaves is indication of sooty mould as well as powdery mildew.
A crabapple tree with one of the above diseases will either wither and die or lack production of edible fruit if not treated.
To help prevent disease, always collect fallen leaves and apples or spray trees in the early season with fungicides.
The apple maggot, winter injury, bark splitting and tree cankers are additional pests and cultural problems of crab apple trees.