I have seen powdery mildew on crape myrtles as I travel throughout the county. Powdery mildew is a common disease on crape myrtles and other ornamental plants.
Powdery mildew first appears as a white to grayish powdery growth, usually on the upper surface of leaves, but it also affects stems, buds and flowers.
The fungi that cause the disease known as powdery mildew attack numerous ornamental plants. Azalea, crape myrtle, dogwood, lilac, rose, zinnia and many other flowers and shrubs are susceptible to powdery mildew.
The disease usually attacks young foliage; however, mature foliage may also be affected. Infected leaves may become distorted, turn yellow and fall prematurely. Infected buds may fail to open. This powdery mildew seldom kills the plant but its infection can limit the plants growth and cause plant decline.
Warm days and cool nights with high humidity favor this disease. It is common in shaded areas and in sites where plants are crowded and air circulation is poor.
Several cultural practices will reduce or prevent the development of powdery mildew. Selecting powdery mildew resistant varieties is the best measure to control the disease. Other cultural measures for control of powdery mildew are to keep plants properly spaced and pruned to promote good air circulation, locate plants where sunlight will be adequate and avoid late-summer applications of nitrogen fertilizer.
Powdery mildew may occur even with the use of cultural control measures, in that case fungicides may be used. For best results fungicides should be applied at the first signs of the disease.
Apply fungicides on a spray schedule to provide continuous protection throughout the growing season.
Be sure to always completely read and follow the fungicide label for use on specific plant species, varieties, rates to be used and timing of application.
Publication ANR 407 “Controlling Powdery Mildew on Ornamentals” gives information about powdery mildew. The publication is available at the Extension Office.
Eddie J. Wheeler works out of the Marshall County Extension Service office on the ground floor of the Guntersville Courthouse. His phone number is (256) 582-2009.