Crepe myrtle bark scale (CMBS) is a small sap-feeding insect that coats the bark of crepe myrtles with white, felt-like coverings and triggers a heavy buildup of black sooty mold. It won’t kill your tree, but it reduces bloom size and quantity while making the trunk and branches look like they’ve been dipped in soot. If your crepe myrtle suddenly looks blackened or you’ve noticed small white patches on the bark, this pest is almost certainly the cause.
How to Identify Crepe Myrtle Bark Scale
The most visible sign is the white or grayish felt-like sacs that cluster along the bark, especially in branch crotches and around pruning wounds. Each sac is roughly 2 mm long, about the size of a grain of rice. These are the egg coverings produced by the adult female, who hides beneath them while feeding. On heavily infested trees, these white crusts can blanket entire stems and become impossible to miss on the smooth trunk.
The simplest confirmation test: press or peel back one of those white coverings with your fingernail. If you see a smear of pink or reddish-purple fluid, or a mass of tiny pink eggs, you’re looking at CMBS. The adult female herself is dark red with short legs and thread-like mouthparts that pierce the bark to feed on sap. The newly hatched nymphs (called crawlers) are also pink and nearly invisible to the naked eye before they develop their own waxy coating.
Adult males look completely different. They’re tiny, gnat-like insects with two wings. You’re unlikely to notice them unless you’re looking closely at the canopy, since male nymphs tend to feed on leaves rather than bark.
Black Sooty Mold: The First Thing Most People Notice
Most gardeners discover CMBS not by spotting the insects themselves, but by noticing that their crepe myrtle’s bark has turned black. As the scale insects feed on sap, they excrete a sticky, sugary substance called honeydew. This honeydew coats the bark, leaves, and anything beneath the tree, and a dark fungus called sooty mold quickly colonizes it. The mold itself doesn’t directly harm the tree, but it blocks sunlight from reaching leaves and makes the entire plant look diseased. Branches, trunks, and even nearby sidewalks can be covered in a sticky black film during heavy infestations.
Life Cycle and Seasonal Timeline
CMBS overwinters as immature nymphs attached to the bark, feeding slowly through the cold months. In late April, the overwintered females begin laying eggs inside their white felt coverings. Each female produces roughly 100 to 300 pink eggs. These hatch about three weeks later, in early May, releasing a wave of tiny pink crawlers that spread along the bark and settle into feeding positions, favoring twig crotches and new growth.
This spring generation matures over the summer and produces a second round of eggs that hatch in September, giving CMBS two generations per year in most climates. On older wood, the insects tend to cluster around branch crotches and pruning scars. On newer growth, crawlers distribute more evenly along the stems. Understanding this timeline matters because the crawler stage, when the insects are exposed and mobile, is the most vulnerable window for control.
Physical and Biological Control
Before reaching for a chemical product, two approaches are worth trying, especially for mild to moderate infestations.
Scrubbing the bark with a soft brush and a diluted dish soap solution physically removes the scale coverings, eggs, and sooty mold. This is labor-intensive on large trees but surprisingly effective on smaller ones. It reduces the population immediately and makes it easier to monitor whether the infestation is returning. Focus on branch crotches, the main trunk, and any areas with heavy white crusting.
Natural predators can also do significant work. Lady beetle larvae are effective biological controls for CMBS. Lacewing larvae and syrphid fly larvae also feed on the scale. In 2024, University of Maryland Extension documented multiple CMBS populations that collapsed or were severely reduced, apparently due to natural predators alone. Some lady beetle larvae (particularly from the Hyperaspis and Cryptolaemus groups) actually look similar to CMBS, so take a close look before scrubbing away anything that seems like scale. If it’s moving, it may be eating your problem for you.
Supporting these beneficial insects means avoiding broad-spectrum pesticide use and planting a variety of flowering plants nearby that provide food for predators at different life stages.
Chemical Treatment Options
For heavy infestations where physical removal and natural predators aren’t keeping up, a soil drench with a systemic insecticide is the most effective chemical approach. The active ingredient dinotefuran, applied as a soil drench in spring as new plant growth begins, is consistently recommended by extension services across the Southeast. The tree’s roots absorb the product, which then moves through the vascular system to where the scale insects are feeding. This method reaches insects hidden under their waxy coverings that contact sprays can’t penetrate.
Timing matters. Spring application, when the tree is actively pushing new growth and pulling water up through its roots, gives the best uptake. Applying too early (before growth starts) or too late (after the tree is in full leaf) reduces effectiveness.
Foliar contact sprays can target the exposed crawler stage in May and September, but they require precise timing to catch crawlers before they settle and produce protective coverings. They’re also less practical on large trees where thorough coverage is difficult.
Pollinator Considerations
Crepe myrtles are heavy bee attractors during bloom, and the systemic insecticides used against CMBS belong to the neonicotinoid class, which is toxic to bees and other pollinators. A soil drench applied in spring will be present in the tree’s tissues when it flowers in summer. This creates a real tension between controlling the scale and protecting pollinators visiting the blooms.
If you choose a systemic treatment, applying it as early in spring as possible (right as growth begins, well before flowering) gives more time for the concentration in pollen and nectar to decrease. Prioritizing physical removal, biological control, and targeted crawler sprays over systemic drenches reduces pollinator exposure. For lightly infested trees, skipping the systemic approach entirely and relying on scrubbing and natural predators is a reasonable strategy, since CMBS won’t kill the tree even if populations persist at low levels.
Long-Term Outlook for Infested Trees
CMBS reduces bloom quantity and size, and the sooty mold is unsightly, but infested crepe myrtles continue to grow and survive. The pest is not a death sentence for the tree. Many gardeners find that a combination of winter bark scrubbing (when the tree is dormant and the scale is easier to see on bare branches), encouraging natural predators, and a single well-timed treatment in spring keeps populations manageable. Monitoring branch crotches and the lower trunk through the growing season helps catch new buildups before they become heavy infestations again.