Apple and Crabapple Diseases
Apples and Crabapples are susceptible to several diseases. The most common are: Apple Scab, Cedar Apple Rust, Fire Blight, and Powdery Mildew. To control these diseases it is important to keep the tree in good health. Proper watering, fertilizing and pruning will help. Remember that trees need an inch of water per week, fertilizing in the spring with a balanced fertilizer (such as 20-20-20) and proper pruning in mid-to late winter. When choosing a crab/apple tree, look for varieties that are disease resistant.
Apple Scab: is a fungal disease, which affects both the leaves and fruit of the crab/apple tree. It causes spots on the leaves and lesions on the fruit. A severely infected tree may completely defoliate. Scab is prevalent when the weather in the spring is wet or humid. This fungus over winters on dead leaves. The wind or splashing rain can transfer it. It is important to rake up and destroy infected leaves and fruit each fall. In the spring, a fungicide can be sprayed at intervals of 7-10 days. Do not spray when the tree is in bloom.
Cedar Apple Rust: is another fungal disease. It infects both crab/apples and certain members of the Juniper family. It causes spots to appear on both the leaves and the fruit. Infected leaves and fruit may drop prematurely. Spores from brown or orange galls on junipers are spread in the spring during wet, mild weather. These spores can travel as far as three miles. This fungus is passed back and forth between the juniper and crab/apple. It is not possible for one crab/apple tree to pass on to another crab/apple. It needs an alternating host. Cedar Apple Rust cannot be controlled on current season’s foliage. As a preventative measure, spray with a fungicide when the buds turn pink and then again when all the petals fall from the blossoms. If possible, do not plant susceptible junipers within several hundred yards of crab/apples.
Fire Blight: is a bacterial disease. It causes blossoms, leaves, and twigs to suddenly wilt and turn black. It may cause young trees to die. It spends the winter in sunken areas (cankers) of an infected tree. In the spring, it oozes from the bark and attracts insects. The insects then pass it on to healthy blossoms. Rain, wind, and pruning tools can also spread this disease. Fire blight spreads rapidly throughout a tree. The best remedy is to prune out any infected twigs or branches 12-15 inch below the infection. Always, sterilize the pruning equipment with a strong bleach solution between each cut to prevent further spreading of this disease. New studies show that crab/apples, which are heavily fertilized in the spring, may be more susceptible to fire blight. The bacteria tend to attack new succulent growth. Too much nitrogen may be a factor. If fertilizing a crab/apple tree that is susceptible to Fire Blight use a 5-10-10.
Powdery Mildew: is another fungal disease. It covers the tops of the leaves with a white film. Generally, powdery mildew is seen late in the summer and is unsightly. It is prevalent during periods of high humidity. Remember to plant crab/apples in full sun with good air circulation. Powdery mildew is not worth treating late in the season. It is best to clean up and destroy all infected leaves in the fall. Spraying the following spring with a fungicide will help control this disease.
Suggestions for Success:
- If you have a crab/apple tree which is susceptible to the above listed diseases, it’s best to start a regular spraying program. Spraying every 10 to 14 days during the growing season will keep many of these diseases under control. Linders recommends Bonides Fruit Tree Spray, which has a fungicide and insecticide combined in one spray.
- If you are looking to plant a crabapple, choose one that has disease resistance. Disease resistant apple trees are more difficult to find. The following is a list of apple trees with some disease resistance: Empire, Fireside, Freedom, Haralred, Liberty, Red Baron, Sweet Sixteen, and Yellow Transparent.