Powder Mildew
Powdery mildews are common fungal diseases on many ornamental plants
in Minnesota. Common hosts are rose, phlox, alpine current, zinnia, begonia,
dogwood, and lilac. In most cases, powdery mildew generally does not seriously
harm the plant.
Symptoms appear on the upper surface of the leaf as white-to-gray powder or dust. Both relative humidity and temperature are factors in the development of the disease. It is most prevalent in cooler temperatures and high humidity. Crowded plants and lack of air circulation are factors in the development of the disease. In Minnesota, increased levels of powdery mildew occur in the Spring and again in the Fall. To help control it, water before noon and avoid wetting the foliage.
When powdery mildew is diagnosed early, control can be achieved by using a fungicide spray, such as Funginex, Benomyl, or sulfur. Fungicides prevent infections from occurring and stop the spread of existing infections. However, they cannot repair the damage that has resulted from powdery mildew. Be sure to read the entire label and follow directions carefully for proper application.
For further information, read online our care sheet on "Fungicide Basics", and "Chemical Basics".
Revised: 03/10/98
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