The Japanese maple (Acer palmatum) is a member of the Aceraceae family. This perennial tree can develop a white powdery coating, known as powdery mildew.
Powdery mildew is a fungal disease occurring most often during the spring and fall months. There are many species of powdery mildew fungi, which affect many ornamental trees, plants and shrubs. Powdery mildew is seldom fatal for trees and plants but is unsightly.
Japanese maple trees with powdery mildew develop white fungal patches on the leaves, flowers, bark and stems. As this disease progresses, black spore-producing bodies appear on affected leaves. Powdery mildew often causes leaves to be curled, stunted, yellow in colour and drop prematurely.
Purchasing trees and plants resistant to powdery mildew is the best way to prevent it. Pruning plant tissue affected by powdery mildew and destroying it helps prevent the spread of disease. Applying fungicides to your Japanese maple trees before rain may help protect your trees from powdery mildew.