by Steven Frank, NC State University
A couple years ago I began warning about a new pest that was spreading throughout crape myrtle country. Now, the crape myrtle bark scale has arrived. From the severity of the infestation it looks like it actually arrived many years ago but now it is “official.” This is bad news because crape myrtles are one of our most commonly planted trees in yards and along streets. Crape myrtles are typically almost maintenance free (unless you top them) but now they will require pest management to stay healthy and beautiful.
Female scales produce fluffy white filaments that cover their body. In spring they produce eggs beneath their body then die. Tiny crawlers hatch from the eggs, settle in their new spot, and begin producing white filaments. They have at least 2 overlapping generations. At low density, crape myrtle bark scale feeds in rough areas around branch collars but as the population increases all the bark may be covered. These scales are most often noticed because trees become covered in black sooty mold. At first many people assume this is from crape myrtle aphids so the scales may go undetected. If you notice unusually heavy honeydew and sooty mold on crape myrtles take a closer look at the bark.
Crape myrtle bark scale is a felt scale related to azalea bark scale and oak eriococcin scale. They feed on phloem like other “soft scales”, thus the honeydew. Even though there is not a lot of efficacy data available drench applications of neonicotinoids are typically effective against phloem feeders. However, since crape myrtles flower continually and attract a slew of pollinators be sure to read the labels for restrictions on using them. Insect growth regulators such as pyriproxyfen and buprofezin are effective for many other scales and may be a good option. Horticultural oil, especially the heavier dormant rate, can reduce scale abundance also.
There are many subdivisions and streets in North Carolina lined with crape myrtles. Inspect these trees to determine when they become infested. Also consider diversifying the tree planting of your neighborhood. Luckily this pest does not kill trees outright like some other exotic pests increasing tree diversity helps ensure all the trees are not infested or killed at once by a single pest.