A Guide to Crepe Myrtles

Crepe myrtles (also crape myrtles), seen by many as something between a bush and a tree, are often misunderstood and, as a result, not well cared for. Properly maintained, however, the crepe myrtle, a beautiful and hardy flowering tree, can be a striking addition to a landscape.

Although native to South Asia, crepe myrtles have been cultivated in North America since the 18th century. Naturally a multi-stemmed bush, the crepe myrtle has been bred into many different species and subspecies, each with its own unique characteristics. The species most commonly found in North Texas is Lagerstroemia indica, which can flower in a range of colors. Left to grow, this species of crepe myrtle can reach a height of about 20 feet, with a spread of about 20 feet as well. Other varieties of crepe myrtle may exhibit different growing patterns and sizes at maturity.

BASIC CARE FOR CREPE MYRTLES

The crepe myrtle is prized for its hardiness, low maintenance, and colorful blooms. Crepe myrtles can thrive in many types of soil, such as the alkaline, dark clay that is present in much of North Texas. Crepe myrtles are also drought resistant, although they can be susceptible to over-watering or poor drainage.

Aside from proper trimming and removal of dead plant matter from crevices between the trunks, crepe myrtles can often benefit from fertilization, and may need professional care when common health issues arise. Fortunately, few of the common crepe myrtle health issues pose a serious threat to the survival of the tree. Attentive pruning is often all that is required to keep a crepe myrtles healthy and vigorous for decades.

Crepe myrtles have thin bark that peels off during the year. As a result, crepe myrtles can be easily damaged by lawnmowers, line trimmers, and other activity. Planting groundcover other than turf grass around crepe myrtles as well as proper mulching can provide a buffer to help protect the trunks and roots.

COMMON CREPE MYRTLE ISSUES

While disease-resistant, the crepe myrtle is not free from pests and health issues. Crepe myrtle “topping,” or removing all growth above a certain height is a common practice and a terrible one. Crepe myrtles have thin bark that peels off during the year. As a result, crepe myrtles can be easily damaged by lawnmowers and other tools. Planting groundcover other than turf grass around crepe myrtles as well as proper mulching can provide a buffer to help protect the trunks and roots.

The crepe myrtle aphid (Tinocallis kahawaluokalani) is the most common crepe myrtle pest. This tiny insect feeds on the sap of the crepe myrtle and produces a liquid called honeydew, that can often be observed dripping from crepe myrtles in the spring. While the aphids generally pose no serious threat to the health of the plant, their honeydew can lead to the growth of sooty mold (see below). Aphids can be controlled with systemic treatments or insecticidal soaps.

While the crepe myrtle aphid has likely been present with the tree since it arrived in North America, issues with scale insects have only recently arisen in crepe myrtles. Crepe myrtle bark scale (“CMBS,” Eriococcus lagerstroemia) was first identified in Texas in 2004, and is now a common pest. CMBS is a miniscule insect that appears as a felt-like gray or white crust on crepe myrtle branches, often on the underside away from the sun. When pressed or screped, CMBS leaves behind a pinkish residue. While research is still ongoing, systemic insecticides (neonictinoids) are currently the most effective control for CMBS. Additionally, washing the affected areas with a solution of mild detergent and water can remove the insects, and slow their spread. Lady beetles (ladybugs) are a good natural control for aphids and scale. Here, the white patches are scale. Sooty mold can ruin the natural beauty of crepe myrtles and develop into a health risk.

Sooty mold is the name given to several different species of fungi that grow on the surface of some plants. When crepe myrtles have aphid or scale infestations, the honeydew produced by the insects provides nourishment for the fungal spores to grow. As the gray fungal mat expands, it can cover leaves and branches. Sooty mold is mostly just an unsightly cosmetic affliction, but in extreme cases can interfere with proper photosynthesis in the leaves. The best way to control sooty mold is to manage the underlying insect activity and honeydew production. As the mold dies, it will be washed away by rain.

Powdery mildew is another fungus (Erysiphe lagerstroemiae) that affects crepe myrtles. Unlike sooty mold, however, powdery mildew can pose a greater risk to the health of the plant. Powdery mildew appears as a grayish-white growth on young plant tissue. Only a few spores are needed, often transmitted by the wind, to take hold and begin an infestation on a crepe myrtle. Cooler temperatures and moderate to high humidity are the idea growing conditions for powdery mildew, so it is most active in the spring and fall. Overwatering, overfertilization, and poor air circulation can contribute a crepe myrtle’s susceptibility to the fungus. As the fungus spreads, it can cause new affected growth to die, with leaves curling and dropping. Extreme cases can cause extensive damage. Fortunately, there are several powdery mildew-resistant cultivars of crepe myrtle. Even without a natural resistance, powdery mildew can be managed or prevented by allowing crepe myrtles to receive full sun, by proper pruning for light and air flow, and by following best practices for watering and fertilizing. Growth that is affected by the powdery mildew fungus should be removed in the fall. Generally, systemic fungicides are not recommended for powdery mildew.