Crape myrtles have been a beautiful low maintenance choice for Mississippi landscapes for many years. Their cinnamon colored bark and brightly colored blooms have made them a favorite. Crape myrtle bark scale (CMBS) is serious insect pest that increasingly threatens the beauty and health of this landscape plant.
CMBS has aggressively spread to twenty-two Mississippi counties, including Lafayette, Pontotoc, and Lee. It is important for gardeners in our area to learn to identify and treat this unsightly pest.
The references for this article include the Mississippi State University Extension Service publications “Crape Myrtle Bark Scale Identification and Control” and “Act Decisively to Stop Crape Myrtle Bark Scale Problems”
What is it?
Heavily infested plants will have limbs and branches that are covered with white felt like patches. CMBS can be positively identified by piercing the felt cover with a toothpick or knife which causes them to bleed a pink substance.
CMBS are spread by wind, animals, landscape equipment, or by transporting infected plants to new locations. When established in an area it spreads easily from one plant to another.
In addition to the white felt like patches, infected crape myrtles will be covered with sooty mold. Sooty mold is a black substance that covers the leaves, branches, and nearby areas. Sooty mold forms from honey dew produced by the CMBS nymphs.
There are currently few natural enemies of CMBS in the U.S. When CMBS is detected, it is important for homeowners to actively apply control measures to limit its spread. The control options for CMBS include avoiding buying infested plants, choosing alternatives to crape myrtles in the landscape, destroying infected plants, or the application of insecticide treatments.
When using insecticides, applying systemic insecticides to the soil around crape myrtles is the most effective method. Systemic insecticides are taken up by the plant and control insects as they feed.
Systemic insecticide products should contain imidacloprid, clothianidin, dinotefuran, or thiamethoxam. The following information about chemical control for CMBS infested areas should be noted: mulch should be removed from around the tree prior to application, it takes several weeks for the treatments to work, all crape myrtles in the landscape must be treated, there will not be 100 percent control, the treatment will need to be repeated yearly, and any previous accumulation of sooty mold will remain after treatment.
Read product labels to determine the best application time and rate. Trees with actively growing leaves can be treated until late September. The ideal time to treat CMBS is from late March through May.
For multi-trunk trees it is often necessary to measure the circumference of each stem at breast height, which is 4.5 feet above the ground. The circumference of each stem should be added to determine the amount of insecticide to use.
Homeowners with several large crape myrtles should consider hiring a licensed commercial pesticide applicator to control CMBS. Commercial applicators have access to cost effective chemical products not available to homeowners.
It is important for homeowners to be aware of the new pest that threatens crape myrtles in our area. Learning how to identify and manage CMBS can slow its spread and allow crape myrtles to continue to be a beautiful part of Mississippi landscapes.