Diagnosing and Treating Crape Myrtle Problems
Crepe Myrtles - Insect and Disease Challenges for Hardy Plants
Oct 3, 2009
Crape Myrtles are popular shrubs in hardiness zones 7 and higher because of their summer-long flowers and the large variety of cultivars described in the Crape Myrtle Quick Guide that range in color from white to dark red and purple, and in sizes from three feet to over 30 feet.
Prevention is the first step in battling Crape Myrtle pests and diseases. Make sure the plant receives at least eight hours of full sun and that it has enough space for air to circulate and keep constant moisture off the branches and leaves. Crape Myrtles do not require a lot of fertilizer or water. So do not over do with care that may kill the plant with kindness.
Disease Problems with Crape Myrtles
Powdery mildew - a common problem on Crape Myrtles, it is rarely fatal to the plant. However it can weaken it and make it more vulnerable to other diseases and pests. As the name implies this fungus leaves a white or grey powdery look on the leaves and stems. A gardener can select varieties that are resistant to powdery mildew. If treatment is necessary, Purdue University Horticulture Department recommends using treatments with low environmental impact such as “horticultural oils, neem oil, or antitranspirants (like Vapor Gard® or Wilt Pruf®).”
Black spot - dark black splotches or spots on plant leaves. Prevention is the first line of defense. Keep the area under the plant free of leaves, remove and burn infected leaves, and do not let water sit on the leaves from overhead irrigation. Use disease resistant cultivars. Spray organic oils as a preventive in the spring. The University of California Horticulture suggests, “A combination of bicarbonate of soda plus horticultural oil can be used to manage black spot (as well as powdery mildew).”
Sooty mold - black staining or powdery coating on leaves and stems. This fungus is attracted by aphids, so treating the aphids is essential. The mold can be washed off the leaves with soap and powered garden hose.
Tip blight - leaves near the stem turn brown. This is a fungus that can be treated with a water-based spray containing appropriate fungicides.
Leaf spot - this condition is caused by the Cercospora fungus which produces yellow spots on the upper leaf surface. Good air circulation can help prevent an attack and treatment with a systemic fungicide may be necessary.
Crape Myrtle Insect Problems
Aphids - often seen beginning in late summer or early fall. These yellow-green insects suck the juice from leaves and create what’s called honey-dew that drips from the leaves like rainfall. These predators can be washed from the leaves with a strong stream of hose water or stopped preventively at the ground level with systemic insecticides. In a severe infection insecticides can be sprayed directly onto the plant. However, this spray will also kill beneficial insects.
Scale - tiny insects that cause white bumps on leaves or branches of shrubs and trees. This is a relatively new problem for crape myrtles and can be deadly to the plant. Texas Cooperative Extension horticulturist Dale Groom suggests watering a scale product into the soil around the plant and using summer-weight horticultural oil followed later in the year with dormant oil spray.
Crape Myrtles are landscape treasures that provide flowers all summer and live long lives. Providing the best growing conditions and taking care of disease and pest problems early will reward gardeners for years to come.
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