There are more than 1,100 fungi species that cause powdery mildew. The disease affects many herbaceous and woody plants.
White powdery patches develop on leaves, young stems, buds, flowers and even fruit. Patches may enlarge until the entire area is covered. The white growth is mycelium and chains of colorless spores. With time, these patches become mealy or felt like and turn gray to tan. Leaves may stunt, curl, become chlorotic and drop early. Flower buds maybe deformed. Damage is more unsightly than harmful on most trees.
Grow resistant plant varieties. Remove all dead or dying plant material. Rake up and destroy all infected dead leaves. Maintain healthy plants. Plant in areas that are proper for the plant species. Do not crowd (allow for good air circulation) plants. Do not work with plants when they are wet. Water as needed during droughts and keep the water off the foliage.
Use fungicide sprays when the problem is severe early in the growing season. Contact your local garden center or your local Cooperative Extension Service office for fungicide recommendations. Fungicides are used as preventives not curative
Written by James Schuster, Extension Educator, Horticulture, and reviewed by Nancy Pataky, Extension Specialist, Plant Pathology, Department of Crop Sciences University of Illinois at Urbana-Champaign.