Crape Myrtle Bark Scale (CMBS) is a significant pest threatening one of the most popular ornamental trees in the southern United States. This invasive insect, first identified in the U.S. in 2004, has rapidly spread, turning the typically low-maintenance crape myrtle into a plant requiring proactive care. Effective CMBS control demands an integrated, multi-step management approach combining physical, cultural, and chemical strategies. The goal is to reduce the existing scale population and prevent future infestations.
Confirming the Infestation: Identification Signs
The first step in controlling the pest is confirming its presence, as other insects can cause similar symptoms. Crape Myrtle Bark Scale is easily identified by small, felt-like insects that are white or gray in color. These insects cluster in branch crotches, along the branches, and on the trunks, often near pruning cuts. Crushing an adult scale will often exude a pink, blood-like liquid, a distinct identifying feature.
A more obvious sign of CMBS is the presence of honeydew, a sticky residue the sap-feeding insects excrete. This sugary substance serves as a growth medium for sooty mold, a black fungus that can coat the bark, branches, and leaves. While sooty mold may also be caused by aphids, the presence of the white, felt-covered scales alongside the black mold confirms the CMBS diagnosis.
Immediate Physical and Cultural Removal Strategies
Before resorting to chemical applications, mechanical and cultural methods can immediately reduce the scale population, particularly for lighter infestations. A soft-bristled brush and a mild solution of water and dish soap can be used to scrub the affected trunks and reachable limbs. This physical action removes adult female scales and their egg masses, eliminating the black sooty mold and improving the tree’s appearance. This scrubbing enhances the effectiveness of subsequent chemical treatments.
Cultural adjustments reduce the pest’s preferred habitat and improve plant health. Removing suckers from the base and using proper pruning techniques increase air circulation and reduce sheltered crevices where scales congregate. Avoid the severe heading back of branches, often called “crape murder,” as this practice weakens the tree and creates entry points for pests. Heavily infested small branches should be pruned and immediately disposed of in sealed bags to prevent the mobile crawler stage from spreading.
Selecting the Right Chemical Treatment
For moderate to severe infestations, chemical control is necessary, often involving a combination of systemic and contact treatments. Systemic insecticides are applied as a soil drench to the root zone. The active ingredients are absorbed and transported throughout the plant’s vascular system, providing long-lasting control as scale insects are killed while feeding on the treated sap.
The optimal timing for a soil drench using products containing active ingredients like dinotefuran or imidacloprid is in early spring as the crape myrtle begins to leaf out, typically from late March through May. Applying the drench before the tree blooms is a safety precaution that minimizes the potential impact on pollinators.
Horticultural oils and contact sprays directly coat and suffocate the insects on the bark surface. Dormant oils, which are heavier concentrations, are best applied during late winter or very early spring before new foliage emerges to avoid leaf burn. For contact sprays to be effective, thorough coverage of the entire bark surface, including under loose bark and in crevices, is essential. Contact insecticides may also be applied in warmer months to target the mobile “crawler” stage, often requiring repeat applications every two weeks to control multiple generations.
Long-Term Management to Prevent Recurrence
Since Crape Myrtle Bark Scale is a persistent pest, the long-term strategy focuses on consistent monitoring and maintaining optimal plant health. Even after successful initial treatment, the tree should be monitored closely during the growing season to catch any signs of re-infestation. Checking the bark and branches monthly aids in early detection, which is the easiest time to manage the problem.
Proper cultural practices, such as ensuring the crape myrtle is planted in a location that receives full sun, can reduce the likelihood of heavy infestations, as scales often thrive better in shadier conditions. Maintaining plant vigor through appropriate watering and fertilization makes the tree more resilient to pest stress. Inspecting any new crape myrtle plants before purchase is an effective exclusion method, preventing the accidental introduction of an infested specimen.