Plant Pathology Infobytes
May 28, 1999
Powdery Mildew on Crape Myrtles - Steps for Control
If grayish-white areas recently appeared on the new growth of your crape myrtles, chances are the problem is powdery mildew. In extreme cases, entire twigs may be blighted by the mildew fungus. While this fungus disease will not kill affected crape myrtles, blighted foliage detracts from the appearance of a popular Southern landscape plant.
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 the mildew. 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 development of this disease. If powdery mildew is showing up in your crape myrtle landscape planting what should be done about it? If infection isn't excessive, infected twigs may simply be removed by pruning. Heavily powdery mildew infected plants will probably require fungicide treatment for full recovery.
Homeowners who have had severe crape myrtle powdery mildew problems in past seasons should start fungicide application 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 crape myrtle powdery mildew, the most effective products are Spectracide Immunex or Immunox. Apply Immunex (1 ½ fl. oz. per gallon of water) every 21 days or Immunox (2 fl. oz. per gallon of water every 14 days) until disease control is obtained. These fungicides may also be used for the control of powdery mildew, and other diseases, on roses, dogwoods, as well as other ornamental plants.
Homeowners who plan to add to their crape 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 Sioux, Biloxi, Comanche, Hopi, Miami, Osage, Pecos, Tuscarora, and Tuskegee. White cultivars include Acoma and Natchez. Lavender cultivars available are Apalachee, Lipan, Muskogee, Wichita, Yuma, and Zuni. Tonto is a red cultivar, which also exhibits good powdery mildew resistance.
Note: When using any fungicide product, read and follow all label directions. If you have questions about powdery mildew of crape myrtle or fungicide application techniques, check with your county Extension office.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.