Crape Myrtle Bark Scale

What are the signs of Crape Myrtle Bark Scale?

When customers contact us about black, sooty mold appearing on crape myrtle leaves, trunks, or even on plants growing beneath the tree, we start by investigating the most common causes. First, we check for aphids. Next, we look closely for crape myrtle bark scale, an increasingly common pest of crape myrtles.

Crape myrtle bark scale is an introduced insect from China, Japan, and Korea. While it is still less common than aphids, we have seen a steady increase in crape myrtle bark scale infestations over the past several years.

Like aphids, crape myrtle bark scale insects feed by sucking sap from plant cells. The insects cannot digest all of the sugars they consume, so they excrete the excess as a sticky substance known as honeydew. This honeydew is often the first visible sign of a crape myrtle bark scale problem.

As honeydew accumulates on leaves and bark, a black fungus called sooty mold begins to grow. Many gardeners mistake sooty mold for a leaf disease, but it is actually a clear indicator of a sap-sucking insect infestation. Aphids and leafhoppers also produce honeydew, so it is always important to inspect the tree carefully to identify the exact pest causing the issue.

Recognizing these early signs of crape myrtle bark scale can help protect your trees and prevent long-term damage.

Sooty Mold and aphids on Crape Myrtle.

What does Crape Myrtle Bark Scale look like?

Crape Myrtle trees that are infested with Crape Myrtle Bark Scale (or CMBS for short) will have immobile white to gray adult scale insects on the bark and twigs. When crushed, this insect will exude a pink substance that will positively identify it as CMBS. There may also be small pink “crawler” scale on the bark or under the female scale insect.

Close up of CMBS and scale insects on twigs. 

Adult female scales attach to tree bark using their mouthparts and begin feeding. As females mature, they secrete whitish to grayish waxy filaments that cover the body. Females lay eggs beneath this covering. The eggs hatch into crawling nymphs. Nymphs move to other parts of the plant or disperse by wind or birds to new trees, where the cycle repeats. In Zone 8, two to three generations occur each year.

How are these insects controlled?

Control of this pest can be difficult. Soil applied neonicotinoids may be used to suppress Crape Myrtle Bark Scale, but it must be applied to the soil at the correct time of year. Make the application just before the Crape Myrtles leaf out in the spring, well before blooms form. This early application will ensure that the product is translocated to the top of the tree as the tree leafs-out. This early use will also minimize the effect the insecticide has on bees, since it is used before blooms appear. (It is never recommended to spray Crape Myrtles with a chemical insecticide when it is blooming, as bees will be affected)

The black sooty mold that appears on the trunk may be removed by using a soft brush and mild soapy water on the trunks. The affected leaves should be raked and bagged when they fall. It may also be beneficial to apply Horticultural Oil at the “dormant season rates” in late February. As always, thoroughly coat all stems and trunks with the oil. Spray when the temperatures are between 45°F and 85°F and the humidity is low. The oil dries quickly and the insects are suffocated.

What if you don’t notice them at the right time to treat them?

If you do not notice this insect until the heat of the summer is upon us, do NOT spray with oil products and do NOT use a systemic insecticide. You can still use a soft brush with a mild soap solution (1 teaspoon Dawn in a quart of water) and scrub it off the trunk. The other methods mentioned above will have to wait for the appropriate time for their use.

Organic Options

Lady beetles consume large numbers of crawler-stage pests, but they usually arrive too late in the season to prevent sooty mold from disfiguring the tree. If you prefer organic options, gently scrub adult scale insects from the trunks with a mild soapy water solution (1 teaspoon Dawn in 1 quart of water) early in spring, before the leaves appear. Then rely on lady beetles to control the pests during the summer months.

Lady Beetle pupae and larvae on Crape Myrtle leaf eating aphids. 

Although Crape Myrtle Bark Scale is rarely fatal, it affects the aesthetics of the tree tremendously. We recommend that you check your trees often to catch it early.