Crapemyrtle, also spelled crape myrtle and crepe myrtle, is an ornamental plant originally native to Asia. In the United States, most specimens are either common crapemyrtle (Lagerstroemia indica), Japanese crapemyrtle (Lagerstroemia faurei) or hybrids of the two species. These plants range from dwarf shrub types to medium-sized trees, and they do best in well drained soils and direct sun. They produce attractive flowers in pink, red, purple or white. Like many other landscape plants, crapemyrtle can suffer from a number of diseases and problems, including yellow leaves.
Many species of crapemyrtle produce leaves that turn yellow or gold in the fall. This natural process is caused by the plant ceasing to produce chlorophyll, exposing the yellow compounds already present in the leaf. White-flowered crapemyrtles usually produce yellow leaves exclusively, while pink or red-flowered varieties may have red, orange or yellow autumn color. One specimen may show several different colors of leaves in the fall, producing a patchwork look.
The crapemyrtle aphid is among this plant's most common pests. These tiny insects grow to be about 1/16 of an inch in length, with a pale green-yellow body and black abdominal spots. Like other aphids, crapemyrtle aphids pierce the plant to consume its sap. They may cause the plant to grow more slowly or develop distorted leaves in small infestations. Large populations of crapemyrtle aphids produce yellow leaves, early leaf drop, and sooty mold growth. Control these insects by encouraging their natural enemies, including ladybugs, or by applying horticultural oil or pyrethroid, organophosphate or carbamate insecticides.
Cercospora Leaf Spot
This disease is caused by the Cercospora lythracearum fungus, and can result in heavy autumn leaf loss. Since it happens when leaves are already changing color and dropping from the crapemyrtle, this disease may be hard to diagnose. Cercospora leaf spot happens on Indian crapemyrtle and its hybrids, and starts as round brown spots about ¼ inch across on the leaf surface. Over time, the leaves may distort or twist. The spots eventually enlarge, turning leave bright red or yellow, then causing them to fall off. Spotting usually starts near the base of the plant and spreads through the canopy to younger growth. The Alabama Cooperative Extension System recommends choosing fungus-resistant cultivars, spacing plants widely, and applying fungicide at 1 to 2 week intervals after spotting appears.
This fungal disease of crapemyrtle causes cottony buff to white patches on leaves, flower buds and new shoots. On plants with a heavy infestation, the shoots and leaves may twist and distort. Powdery mildew also causes flower bud abortion, keeping the plants from blooming. On susceptible cultivars, the shoot tips and leaves may turn yellow, wither and fall off. This condition may appear as early as mid-April, but usually goes unnoticed until May or the beginning of June. To combat powdery mildew, provide plenty of ventilation around plants, avoid allowing water to remain on the leaves overnight, and apply fungicide shortly after the plants leaf out, at 1- to 2-week intervals until midsummer.