Black Spots on Blueberry Leaves

Leaf Spot

• Blueberries are vulnerable to several types of leaf spot that can appear as black or dark-colored spots on leaves. They include Septoria, Anthracnose, Gloeocercospora, double spot and Alternaria leaf spot. Each of these are caused by a fungus. They often start as small spots or flecks on the blueberry leaf, and then grow into larger lesions, spreading to stems and buds.

Causes

• Over-watering, insect infestations, wounds on the plants and leaves as well as proximity to other infected plants can cause blueberry bushes to become infected with leaf spots. Since leaf spot diseases are caused by a fungus, they can also be spread by the wind, with spores traveling from plant to plant. Often in the home garden, leaf spot affects not only blueberries but other susceptible plants such as tomatoes and peppers.

Treatment

• Fungicides are effective at treating leaf spot if they are applied early. Treatment should begin at the first sign of black or unusual spots on the blueberry bushes. If leaf spots have been a problem in past seasons, a preventive treatment in the spring may be effective. Prune away as many infected areas as possible. Remove any dead leaves or twigs underneath the bush.

Prevention

• Keep blueberry bushes trimmed so that they are not touching each other and so there is plenty of air circulation around each bush. Avoid watering in the evening, and use soaker-type watering methods if possible so that water is not allowed to remain on the leaves. Trim away any leaves that are touching or near the ground.