It is probably infected with apple scab; keep reading for more information on scab and other crabapple problems.
Crabapples represent a diverse group of small ornamental trees with varied growth habit, flower color, and fruit. This group of trees adapts to a wide range of growing conditions. Unfortunately, some of the older cultivars are susceptible to several diseases. The best way to avoid these diseases is to plant disease-resistant cultivars. Conact your local Extension office for a list of crabapples for your area.
Scab is the most common disease of crabapple. Olive-brown leaf spots appear shortly after bloom. Severe infection may result in significant leaf drop. Trees that experience this damage each year may be weakened and grow slowly. Trees susceptible to scab often produce unsightly water sprouts to compensate for leaf loss. Because repetitive fungicide sprays would have to be used to prevent damage, this method of control is rarely used in landscapes.
Fire blight is a bacterial disease that may rapidly kill bud clusters and young shoots. Infected shoots may turn black and wilt, giving a shepherd's crook appearance. Infection usually takes place during bloom, but it may continue through early summer. Prune out diseased shoots well below the blighted area. Disinfect shears often with 10 percent household bleach or other disinfectant. Do not fertilize with high nitrogen fertilizers because succulent growth is most susceptible to disease.
Cedar-apple rust infections on crabapple appear as yellow-gold leaf spots. Rust spores from neighboring junipers infect leaves and fruit during mid- to late spring.
Powdery mildew appears on young shoots as white, powdery growth. Infected shoots may be distorted and stunted. At the first sign of disease, spray with a fungicide. Ask your Extension office for specific advice on fungicides.
Frog-eye leaf spot appears as brown to gray spots on leaves and fruit, usually in mid- to late summer. Because it doesn't cause leaf drop, damage is usually minimal.
