Plant Pathology Infobytes

May 19, 1998
Powdery Mildew Widespread on Crepe Myrtles

Grayish white patches on the new growth of crepe myrtles is an indication of the presence of powdery mildew. This fungus disease has made its appearance during the past few weeks, and although powdery mildew won't kill affected plants, it is unsightly and weakens crepe myrtles by attacking young leaves and growing tips.

Leaves infected early in the season by the powdery mildew fungus become curled and distorted as they expand. Infected younger leaves have blister-like areas which quickly become covered with a grayish-white powdery growth. On older leaves, large white patches of fungus growth appear, but there is little leaf distortion. Flowers which originate from infected buds often become blighted.

Powdery mildew has been more common this season because of dry weather, warm days and cool nights -- conditions which favor its development. If powdery mildew is showing up in your crepe myrtle landscape planting what should be done about it?

Control of powdery mildew should begin with fungicide applications as new growth emerges in the spring or immediately after the first sign of the disease. It may be necessary to continue fungicide sprays until leaves are mature, at which time they are less susceptible to the powdery mildew fungus. Also, fungicide applications can be made during the flowering period to prevent blossom blight infection.

Although several fungicides help reduce crepe myrtle powdery mildew, the most effective product is Spectracide Immunex. Used at the rate of 1 1/2 fl. oz. per gallon of water, this fungicide provides excellent control when applied to infected plants.

This fungicide may also be used for the control of powdery mildew on roses, dogwoods, and other ornamental plants. Spectracide Immunex is also an excellent fungicide for control of black spot of rose.

Homeowners who plan to add to their crepe myrtle plantings should consider using varieties which are resistant to powdery mildew. Such cultivars are now available in nurseries and garden centers. Some of the pink cultivars include Biloxi, Comanche, Hopi, Miami, Osage, Pecos, Sioux, Tuscarora, and Tuskegee. White cultivars include Acoma and Natchez. Lavender cultivars available are Apalachee, Lipan, Muskogee, Wichita, Yuma, and Zuni.

Note: When using any fungicide product, read and follow all label directions. If you have questions about powdery mildew of crane myrtle or fungicide application techniques, check with us as the County Extension Office.


Written by the late Dr. Frank Killebrew

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