Crapemyrtle bark scale

Although Crapemyrtle bark scale  is rarely fatal to affected trees and shrubs, it diminishes their appearance by depositing honeydew on the branches and foliage, which encourages the growth of black sooty mold.

As if the drought hasn’t been hard enough for gardeners to deal with, an exotic invasive insect pest from Asia is wreaking havoc on crapemyrtles planted across Oklahoma. First detected in northern Texas in the early 2000s, crapemyrtle bark scale is spreading across much of the southern United States and has been reported in multiple counties in Oklahoma.

Although CMBS is rarely fatal to affected trees and shrubs, it diminishes their appearance by depositing honeydew on the branches and foliage, which encourages the growth of black sooty mold. Infested plants exhibit inferior aesthetic quality, as well as reduced flower size and quantity. Crawlers, or nymphs, are spread throughout the landscape quite easily via wind, so once it is established in a new area it can move quickly.

Crapemyrtle is a popular landscape plant many homeowners want to establish in their landscapes. Because the rapid spread of CMBS in the southern U.S. is mainly due to movement of infested nursery stock, it’s important to be able to identify this pest when shopping for new plants.

Closely related to azalea bark scale, adult females are white to gray and felt like, and can be found encrusting twigs and trunks of crapemyrtles. Initial detection is usually made by the homeowner who notices the presence of black sooty mold on the plant. This pest can sometimes be misdiagnosed as crapemyrtle aphid. However, the appearance of white scale bodies on the bark and associated pink liquid when they are crushed are tell-tale signs of CMBS. As they mature, these pests secrete waxy deposits that become felted or matted into a thick white/gray scale covering. The females lay eggs under the scale from May through September, then the crawlers emerge and disperse to new areas of the same plant or are windblown to new host plants.

CMBS is difficult to control without the use of systemic insecticides, which are used to control most sucking pets. However, systemic insecticides, which are products that contain imidacloprid, dinotefuran, clothianidin and thiamethoxam, aren’t recommended for the control of CMBS because of the risk these ingredients pose to pollinating insects such as honeybees and bumblebees. It’s also risky for the long-flowering period of crapemyrtles that extends through most of the growing season.

Some other less toxic methods of control include:

1. Inspecting crapemyrtles prior to purchase for signs of CMBS.

2. Scrub the bark of infested plants with a soft brush and a mild solution of dishwashing soap and water. Washing removes many of the female scales and egg masses, as well as buildup of black sooty mold on branches and trunks.

3. Horticulture oil may be effective when applied during the winter at a dormant application rate. Be sure to use enough oil to reach behind loose bark, branch crotches and other crevices.

4. Lady beetles in the genus Chilocorus are effective predators of many scale insects. Unfortunately, predation of CMBS occurs too late in the season for effective reduction of black sooty mold growth.

Contact your county Oklahoma State University Extension educator or nursery professional for more information.

David Hillock is a consumer horticulturist with OSU cooperative extension.

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