Powdery mildew is a fungus that grows on upper leaf surfaces and stems. This white powdery coating can be a problem in the spring on many flowers, trees and woody shrubs. Young leaves, shoots, flowers, buds and fruit usually are targets of the disease. Outbreaks mostly occur in humid, shaded areas.

Seriously infected plants may have yellow foliage, leaf rolling, early leaf drop and slowed plant growth. Damage to developing flower buds also may greatly reduce floral quality.

Planting powdery mildew-resistant varieties is one way to control the disease, says Jackie Mullen, a plant pathologist with the Alabama Cooperative Extension System. Pruning any overhanging limbs or branches on trees and shrubs improves air circulation around ornamentals, and the sunlight may help slow the spread of the disease.

Another effective control method is to apply fungicide treatments to plants as soon as powdery mildew appears on foliage. Always follow label recommendations when applying fungicides.