Powdery Mildew

There are several types of powdery mildew fungi and they all produce similar symptoms on plants. The main characteristics are spots or patches of white to grayish, talcum-powder like growth. Powdery mildew has tiny, pinhead-sized & spherical fruiting structures that are at first white, and later go from yellow-brown to black. It can be in a group or by itself.

It is usually most apparent on the upper sides of leaves but will also affect the bottom sides as well. Also affected are young stems, buds, flowers, and young fruit. Infected leaves and plant parts can become distorted, turn yellow with small patches of green, and can fall prematurely. Also, infected buds may fail to open.

Powdery Mildew Conditions:

The severity of powdery mildew depends on a variety of factors including the host plant, age of the plant, condition, and weather factors during the growing season. Powdery mildews are most severe in warm, dry climates because the fungus does not need te presence of water on the leaf for infection to occur. High relative humidity does greatly favor powdery mildew and it thrives in crowded conditions where air circulation is poor.

Controlling Powdery Mildew:

Cultural – Many plants such as roses, vegetables, and Kentucky Bluegrass have been developed to be tolerant and resistant to powdery mildew. Buying a resistant plant variety can help in your control efforts. Other methods can include avoiding overhead watering to keep relative humidity down and removing infected plants.

Chemicals - If natural methods don’t do the job, an application of fungicide might be the only way. Before using chemicals, consider contacting a local county extension agent or master gardener for regional advice. Chemical are most effective when combined with cultural controls.