Serviceberries (Amelanchier spp.) are deciduous shrubs or small trees that produce small edible berries and bloom in clusters of white or pink blossoms during spring. The serviceberry also is known for its purplish new leaves in spring that turn dark green in summer and yellow, orange or reddish in autumn. Serviceberries are susceptible to a few fungal diseases.
Entomosporium Leaf Spot
The fungus Entomosporium leaf spot causes tiny reddish spots often surrounded with yellow halos on the leaves of serviceberries. The leaf spots grow larger and darken, followed by dark spore bodies forming in the centers of the spots. The leaves may drop prematurely. Treatment of Entomosporium leaf spot begins with removing and discarding all of the diseased leaves from the serviceberry, as well as raking up and discarding any fallen leaves. Prune to thin out lower branches to increase air circulation around the serviceberry, and avoid spraying the foliage with water. If the infection becomes severe, apply a copper-based fungicide or chlorothalonil to the serviceberry according to the label's instructions.
Rusts are also fungal diseases that cause dry reddish, yellowish or orange-colored pustule spore masses on the serviceberry’s leaves, especially on the undersides. The upper leaf surfaces tend to turn yellow to brown, and in some cases leaves may become distorted and discolored. Galls or swellings also can appear with cankers on the bark, twigs and branches. Cure rusts by raking away and discarding all fallen infected leaves and pruning away infected shoots and branches from the serviceberry. Don’t perform any overhead watering or get the foliage of the tree wet. Apply an appropriate fungicide in spring, according to the directions on the label. The serviceberry is most susceptible to cedar serviceberry rust or “witches-broom” disease.
Powdery mildew can affect most types of fruit or berry trees and shrubs, causing a white to grayish, powdery spore-like coating on both sides of the leaves, as well as sometimes the shoots, flowers or fruits. Powdery mildew most commonly appears during warm, moist conditions, and its spores can over-winter on serviceberries. Prune away and discard all diseased growth on the serviceberry to control the spread of the disease. Spray the serviceberry with horticultural oils or neem oil to get rid of a severe powdery mildew infection. Spray the serviceberry when the tree isn’t stressed from drought and temperatures aren’t hotter than 90 degrees Fahrenheit. Don’t apply the horticultural or neem oils within two weeks of applying any type of sulfur spray.