By Earl ‘Bud’ Reaves, Anne Arundel Forester
One of the most popular flowering trees in Maryland is the Crapemyrtle (Lagerstroemia indica). Producing an abundance of showy flowers in late summer and early fall, it brings a splash of color when most trees and shrubs are going dormant. It also has a pleasing, smooth bark, which reveals multiple colors as it peels. It is one of the nursery industries biggest sellers and because of its general lack of diseases and insect pests in our area is an easy plant to maintain in the landscape. That has changed dramatically with the detection of Crapemyrtle bark scale (Acanthococcus lagerstroemiae), a scale insect that covers the bark of crapemyrtles, and feeds on the sap of the tree. This pest has also been detected on other plants, including beauty berry, a Maryland native, and soybeans. Because of the potential spread to native plants and serious damage to a popular landscape plant, the Crapemyrtle bark scale has been selected as this month’s Maryland Invasives Species Council Invader of the Month.
Crapemyrtle bark scale was first detected in the United States in central Texas in 2004. It has since spread East and north to Virginia and Delaware. It has now been documented in Maryland.
Crapemyrtle bark scale is a bark or felt scale, slightly different than a soft scale insect, but like soft scales produce a waxy coating to protect the larvae, adults and their eggs. These are small insects, no more than 2 millimeters in length. Females do not move once they attach to the twig or branch. Males are winged and fly to the females to mate. Once the females produce an ovisac, or egg case, they die, leaving the eggs protected under the waxy coating. When they hatch, the nymphs or ‘crawlers’ will move to a fresh site on the twig and start the cycle over again. As with most scale insects, they are most vulnerable in the crawler stage. They can attach anywhere there is room on the twig or branch and will concentrate around pruning cuts. There are 2 to 4 generations in a year, reproducing rapidly. The number of generations in Maryland and Delaware have not been documented, however, researchers Dr.’s Stanton Gill of University of Maryland Extension, and Brian Kunkel, of University of Delaware have a study in progress to determine this. Crapemyrtle bark scale also produces copious amounts of “honey dew,” a secretion which attracts insects feeding on the sugars in the extract, and also provides a medium for sooty mold, that stains the foliage and bark, leaving an unsightly appearance. Crapemyrtle bark scale can be fatal in extreme situations. In most instances however, the effect is a combination of a degraded visual appearance, and the weakening of the tree.
Crapemyrtle bark scale is not just found on its namesake. It has been found on American beautyberry, a popular shrub often used in landscape and restoration plantings. Potentially, there are up to 30 different plants that could be a host for this insect, including persimmon and soybeans. The impacts on crapemyrtle alone is enough to cause concern as it is one of the most popular choices as a flowering small tree in landscapes in Maryland. Crapemyrtle is popular not only for its flowering ability but also for its general lack of insect pests, with crapemyrtle aphids being the other pest that causes problems. This insect pest will increase the need for maintenance, including pesticide use.
Crapemyrtle itself is a nonnative invasive species with documentation in most of the southeastern states including Maryland. Fortunately, it is not as aggressive as other invasive tree species. The best way to avoid Crapemyrtle bark scale is not to plant crapemyrtles. There are native alternatives such as service berry Amelanchier arborea, flowering dogwood Cornus florida, redbud Cercis canadensis, and witch hazel, Hamamelis virginiana L. that have showy flowers as well. If you already have crapemyrtles, check for infestations and if severe, contact a certified arborist. Control in light infestations may just require spraying a with a garden hose to wash them off the branches and twigs. This can also alleviate the sooty mold that grows on the honeydew that they produce in abundant amounts.
Severe cases may require the use of pesticides. Horticultural oil and insecticidal soaps are often used on scale insects. Insecticides such as the neonicotinoids can also be used on soft scales but must be applied by professionals. Because of the risk of harming pollinators when using neonicotinoids, growth regulating pesticides such as pyriproxyfen (trade name -Distance) and Buprofezin (trade name – Talus), which interfere with the development of the larvae and \or eggs to maturity, are recommended from an Integrated Pest Management position. Pesticides must be used according to the label, and while wearing personal protection equipment to protect the applicator. If help is needed, contact your agricultural extension agent or a licensed commercial applicator.
It is believed that this invasive pest will spread rapidly throughout Maryland in the coming years. Careful monitoring and measures taken to control it will lessen the impact it will have on one of the most popular ornamental trees in Maryland.