The crepe myrtle (Lagerstroemia spp.) genus is a truly spectacular member of the loosestrife family, boasting a flowering season that may last up to 120 days. The beauty of the shrub's flowers, which may be pink, lavender, white, purple or red, is undermined by damaged foliage. A crepe myrtle with yellow, wilted foliage is likely battling against a disease or cultural problem.
Excessive nutrients, pesticides and herbicides in the soil and in the air can cause toxicity symptoms in crepe myrtle. Foliage may wilt and die or turn yellow at the edges. Branches may die back, and the shrub's weakened state may invite pests, exacerbating the problem. Plant crepe myrtle in well-draining soil to help root development and use caution when applying herbicides, such as not spraying them on windy days when they can drift onto desirable plants.
Cercospora leaf spot is a fungal disease that is most active in warm, moist weather. The disease attacks foliage, causing yellow spots and sometimes, defoliation. Avoid crowding crepe myrtle against buildings, structures or other plants, as poor air circulation facilitates the disease. Consider planting a leaf spot resistant cultivar such as "Fantasy (Lagerstroemia fauriei "Fantasy"), a white-flowered Japanese crepe myrtle cultivar suitable for U.S. Department of Agriculture plant hardiness zones 6B to 10A.
Bacterial leaf scorch is a fatal disease similar to oleander leaf scorch that has no cure, according to the University of California Statewide Integrated Pest Management Program. Disease symptoms resemble water stress, and include yellow and wilted leaves. Leaves affected by bacterial leaf scorch will initially be yellow at the tips or margins. The disease is spread by glassy-winged sharpshooter insects, which unfortunately cannot be controlled by insecticides. Infected shrubs should be removed to prevent spread to healthy plants.
Crepe myrtle will suffer if not grown in the proper cultural conditions, and foliage problems may occur as a result. Hardiness varies depending on species. Common crepe myrtle (Lagerstroemia indica) may be grown in USDA zones 7 to 9. Crepe myrtles require bright, sunny situations and well-draining, moist soil. Established plants can tolerate some drought but should be watered during extended dry periods. Remove spent flowers to encourage a second flush of blooms, and prune in late winter or early spring to remove dead or diseased branches.
- University of California Statewide Integrated Pest Management Program: Oleander Leaf Scorch
- Clemson Cooperative Extension: Crape Myrtle Diseases & Insect Pests
- Floridata: Lagerstroemia Indica
- University of California Statewide Integrated Pest Management Program: Nutrient and Mineral Excesses
- University of Florida Extension: Lagerstroemia Fauriei