Crabapple trees are a variety of 30 to 35 different deciduous trees and shrubs that produce lovely flowers and small berries that are often called wild apples or crab apples. Several varieties of crabapple are susceptible to severe disease such as apple scab and apple rust.
Choose resistant trees to help fight crabapple disease. Cultivars, plants which have been raised to be disease resistant, are the best trees to plant in an area to prevent disease and the spread of disease to other plants. Crabapple trees with a high resistance include Ann E., Basakatong, Bob White, Jack, Japanese Flowering, Louisa and Prairie Maid.
Cultural practices applied to your crabapple tree will prevent the conditions that breed and spread disease. Fallen leaves create moist areas and decay which feed fungi that causes many crabapple diseases. Rake and destroy leaves that fall underneath the tree before they become brittle and break apart, to prevent disease conditions. Remove fallen fruit as well. Pruning the crabapple tree in late winter to open up the canopy allows drying winds to get inside the tree and prevent moist conditions.
Spray crabapple trees that are susceptible to disease infection. Spraying done on a regular schedule prevents the buildup of fungal spores. Integral to disease prevention is the application of fungicide and insecticide in the spring, between April and May. The best time to apply is before first bloom when the buds begin to show pink. Apply further applications every 7 to 10 days, with the shorter interval preferable during wet weather.