by Wizzie Brown
Crape myrtles are a popular landscape tree in parts of Texas; prized for their beauty. While this tree has been relatively maintenance free for years, that is no longer the case now that crape myrtle bark scale (CMBS) has been found in Texas.
Crape myrtle bark scales are small, wingless insects, pinkish in color and covered with a white, velvety covering. When you look at the bark of an infested tree, look for round to oval shaped white velvety insects. If you puncture one with a toothpick, it will exude a pink substance.
When inspecting crape myrtles for CMBS, look along trunks, limbs, as well as smaller twigs and branches found towards the top of the tree. You’ll want to look for scale insects and sooty mold. Sooty mold is a black colored fungus that grows on honeydew; honeydew is an excretion from scale insects (and other small, soft-bodied insects such as aphids and mealybugs).
Heavily infested crape myrtles have CMBS that produce copious amounts of honeydew on the tree and surrounding area which leads to growth of sooty mold, turning landscape plants black. Infested crape myrtles produce fewer and smaller blooms, although it may be difficult to tell unless you have an uninfected tree to compare.
Only male crape myrtle bark scales fly. Others are dispersed by wind, birds, other insects, or landscape maintenance equipment to nearby areas. Long-distance transport occurs via infested material. Once CMBS are in an area, they can move on to nearby trees.
Control options are varied for CMBS. There are lady bugs that eat CMBS, but this may take time for control as the ladybug population is tied to the population of insects they feed upon. Ensure that if you buy and plant crape myrtles, that you inspect them and not plant any infested trees. You might even consider selecting a different species of tree or shrub for the landscape.
Pesticide treatment for crape myrtle bark scale can be done with either a contact spray or a systemic. Studies from TAMU discovered that contact sprays should be used when pest numbers are peaking (crawler/ nymph numbers peak mid-April through May), and two treatments should be done with the second treatment taking place two weeks after the initial treatment. Insecticides with bifenthrin as the active ingredient tend to work best.
Systemic treatments should be applied earlier, when the leaves are budding out. Systemics such as imidacloprid and dinotefuran are best used as a soil treatment in March so that they are taken up by the tree and in place for the crawler population in April-May. These products should be used when trees are NOT in bloom to protect pollinators.
For a video on how to treat crape myrtles for CMBS, you should go to this link:
https://citybugs.tamu.edu/2018/08/28/how-to-treat-your-crapemyrtle-for-bark-scale/
For more information or help with identification, contact Wizzie Brown, Texas A&M AgriLife Extension Service Program Specialist at 512.854.9600. Check out my blog at www.urban-ipm.blogspot.com
This work is supported by Crops Protection and Pest Management Competitive Grants Program [grant no. 2017-70006-27188 /project accession no. 1013905] from the USDA National Institute of Food and Agriculture.