How to identify crape myrtle bark scale?
Crape myrtle bark scale (Acanthococcus lagerstroemiae), or CMBS, was first reported in North America around 2004, and has spread rapidly wherever crape myrtles grow. Its damage is rarely fatal to otherwise healthy crape myrtles (Lagerstroemia spp. and hybrids), but it’s unsightly and can reduce vigor and flowering. In severe cases you might see stunted growth or a few dead branches.
In Southern climates, there can be up to four generations of this sap-sucking scale insect per year. So you might find different stages on a tree at any time. Small, feltlike white or pale gray egg sacs hang along branches. Eventually they open, each releasing up to 300 pink nymphs, which crawl and fasten themselves to the bark to begin feeding. Some may be carried to other crape myrtle trees by wind or water.
As the adults feed, they excrete a sweet, sticky honeydew. It sticks to crape myrtle’s leaves and bark (and anything else underneath), eventually turning to a sooty black mold.
How to get rid of crape myrtle bark scale
Horticultural oils will suffocate CMBS at any stage of life. Read the label to determine the right mixture for the time of year. But before you spray, scrub off some of the worst infestation with soapy water and a stiff brush.
Because there can be several generations each year, timing is hard to determine. You’ll most likely need to spray several times during the growing season. Scientists are investigating biological controls, and plant breeders are working toward CMBS-resistant crape myrtles. But at this point, research is ongoing.
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