Crepe Myrtle Bark Scale (CMBS) is an invasive insect that has become a serious concern for a widely beloved landscape tree. This nonnative pest, first detected in the United States in 2004, threatens to turn the crepe myrtle from a low-maintenance feature into an unsightly, high-maintenance burden. It typically appears as a unique, felted white or gray encrustation on the bark, feeding primarily on plant sap. The insect’s activity leads directly to a secondary problem: the development of black sooty mold. This guide provides a clear, actionable strategy for removing the scale and restoring the health and beauty of your crepe myrtles.
Identifying Crepe Myrtle Bark Scale
The presence of CMBS is often first indicated by a sticky, sugary liquid called honeydew accumulating on the branches, leaves, and ground beneath the tree. This honeydew is the sugary waste product excreted by the feeding insects. A dark fungus, known as sooty mold, then grows over this residue, blackening the trunk and branches.
The scale insects are small, pinkish-white to gray bumps, covered in a distinctive white, felt-like or waxy coating. They cluster in protected areas, such as branch crotches and around pruning wounds. Crushing one of these white coverings reveals a pink or reddish liquid, confirming CMBS identification. While the sooty mold does not harm the plant tissue, its presence signals a heavy infestation of sap-feeding scale insects.
Immediate Physical and Mechanical Removal
For accessible, smaller trees or low-level infestations, mechanical removal is the most immediate, non-chemical way to reduce the scale population. This involves physically dislodging the protective white coverings and the adult scales from the bark. A soft-bristled brush, sponge, or rag can be used with a mild solution of soapy water to scrub the infested areas.
A simple solution can be made by mixing approximately one to two tablespoons of liquid dish soap into one gallon of water. Use this mixture to thoroughly scrub the trunk and reachable limbs, taking care not to scrub so vigorously that you damage the crepe myrtle’s naturally thin, exfoliating bark. The washing action removes many of the mature female scales and their egg masses, which are protected from many topical sprays by their waxy coating.
For higher branches, a strong jet from a garden hose can also be used to wash off the sooty mold and dislodge some of the insects. Pruning out small branches that are heavily encrusted with scale is also an effective way to remove a large number of insects at once. Immediately bag and dispose of any pruned, infested material to prevent the spread of the scale to other nearby plants.
Chemical and Systemic Treatment Options
For moderate to severe infestations, chemical approaches offer the most effective long-term eradication. These methods must be carefully timed to target the most vulnerable stages of the insect’s life cycle. The first strategy involves using contact sprays to suffocate overwintering nymphs and adults.
Horticultural Oil Application
Dormant oil, a heavier formulation of horticultural oil, should be applied in late winter or very early spring before buds break and new leaves emerge. This suffocates overwintering scales by coating them in a thick layer of oil. Thorough coverage is necessary, especially coating the branch crotches and crevices where insects shelter. Apply dormant oil only when temperatures are consistently above 45°F and below 90°F to ensure effectiveness and avoid damaging the plant.
Systemic Insecticide Soil Drench
The most effective, long-lasting treatment uses systemic insecticides applied as a soil drench around the base of the tree. Products containing active ingredients such as dinotefuran or imidacloprid are absorbed by the roots and translocated throughout the plant’s vascular system. This makes the plant sap toxic to the sap-feeding scale insects for an extended period.
The ideal time for application is in the early spring, typically from late March through May, as the crepe myrtle begins to leaf out. This timing is important because it allows the insecticide to move fully into the plant before the scale’s mobile “crawler” stage begins to disperse.
Dinotefuran offers faster uptake and quicker control, while imidacloprid generally provides a longer residual effect, sometimes lasting up to a full year. Always follow the product label instructions precisely to determine the correct dosage, which is usually based on the cumulative trunk diameter of the tree.
Long-Term Prevention and Maintenance
Sustained management requires cultural practices that make the crepe myrtle less susceptible to future infestations. When planting, select a location that provides full sun and good air circulation, which helps reduce the humidity that scale pests prefer. Inspect all new crepe myrtle purchases carefully, checking the branches for signs of the white, felt-like scale before bringing them into your landscape.
Pruning for good structure encourages healthy growth and allows for better spray coverage if chemical treatments are needed. Avoid excessive pruning, as the resulting dense, soft growth can be more attractive to pests. Keeping the area around the base of the tree clean by removing leaf litter and weeds also supports tree health. Regular monitoring, especially in the branch crotches, allows for early detection and treatment before a minor infestation becomes a major problem.