Podosphaera leucotricha General Information . This fungal disease occurs wherever apples are grown and is particularly severe in the arid regions of the western United States. Powdery mildew can be particularly severe in nurseries. Severity of the disease depends upon present and past weather conditions, cultivar, and control procedures. Although the disease does not kill trees per se, losses can be severe if fruit russetting occurs.
Red delicious is relatively resistant to mildew.
Pear powdery mildew is also caused by this fungus Symptoms . The fungus can infect apple leaves, blossoms, and fruit. Whitish, feltlike patches of fungal mycelium on the lower surface are often the first indication of infection. The lesions may appear as chlorotic spots on the upper leaf surface. Eventually they can spread and cover the entire leaf with a white, mealy coating.