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(Article for September 2026. This is an edited and combined version of two articles published separately in local news media.)
In the last article, I discussed what crapemyrtle bark scale (CMBS) is. Here I discuss its management.
First, if you’re thinking about planting a crape myrtle, consider whether you may want to choose an alternative. A couple of plants that fill a similar role in the landscape (small, flowering trees for sunny sites) include chaste tree (Vitex agnus-castus) and large cultivars of Chinese fringe flower (Loropetalum chinense), pruned into a tree form.
If you do decide you want to plant a crape myrtle, check the trunks and branches before bringing it into your landscape. Certainly, avoid plants that have black sooty mold on the trunk, but also check for the small, cottony coverings of certain CMBS life stages. As mentioned in the last article, the life stages that have the white coverings are immobile, so if you poke it and it moves on its own, it’s not CMBS. (On the other hand, it could be a beneficial insect that feeds on CMBS, such as Hyperaspis bigeminata.)
Choose a sunny site for your crape myrtle. Full sun exposure may reduce CMBS as well as promote more flowering.
Washing trunks of crape myrtles with a soft brush and mild soapy water can help remove CMBS and associated sooty mold. This is unlikely to get rid of all CMBS individuals, but it can quickly improve the appearance of the plant and reduce the number of insects.
Sometimes, certain shoots have particularly heavy infestations, so you can prune out and dispose of these. Of course, if you don’t want to deal with CMBS at all, you can remove the plant.
There is no ideal insecticide-based management approach for CMBS. The easiest and, to my knowledge, most consistently effective way to treat it is with a soil-applied insecticide drench containing imidacloprid or another insecticide in the neonicotinoid group, such as dinotefuran or thiamethoxam.
These insecticides move up into the plant from the roots and remain in the plant for a long time (over a year). Pest insects come in contact with the insecticide when they feed on the plant. Beneficial insects that just rest on the plant are not affected. However, they can be exposed to insecticide residues if they feed on pollen or nectar from the plant, on pest insects, or on honeydew excreted by pest insects. (Crape myrtles don’t produce nectar, but they do have pollen.)
Among the neonicotinoid insecticides, imidacloprid products are most readily available. There are several home garden insecticide products that contain imidacloprid as the active ingredient and are labeled for soil drench applications around ornamental trees and shrubs. Examples include Bioadvanced 12 Month Tree & Shrub Insect Control Concentrate, Bonide Annual Tree & Shrub Insect Control with Systemaxx, Ferti-lome Tree & Shrub Drench, and Monterey Once a Year Insect Control II. These can be applied once per year.
Sources typically recommend using these systemic, drench-applied products in the spring.
In contrast with the ease of using a soil-applied drench, successfully treating scale insect infestations with insecticides sprayed onto the trunks and branches can be tricky. Once they have their waxy coverings, they’re largely protected from chemical sprays. The young, crawler stage of the insect that is most susceptible to insecticides is only present at certain times of the year and isn’t easily seen.
Since some common insecticides are not effective on CMBS at most times during their lifecycle but do kill beneficial insects that feed on pest insects, the use of such insecticides can actually cause an increase in CMBS populations.
The time of year at which crawler populations are greatest varies from year to year and location to location, but in Louisiana, it appears that the first peak can generally be expected in April or May. You can use double-sided tape to check for their presence, if desired. CMBS crawlers are about 0.5 mm long and pink in color.
To reduce the impact on beneficial insects in comparison to some conventional insecticides, you can use an insect growth regulator (IGR) containing pyriproxyfen (Distance, Fulcrum, or another product labeled for use on ornamentals) twice during the time when crawlers are present, following label directions. These products are not sold in home garden-sized products but can be purchased by anyone. (Talus 70DF [buprofezin] is another IGR option but isn’t labeled for use in residential areas.)
Bifenthrin products such as Bifen I/T, Bioadvanced Tree and Shrub Insect Killer Spray Concentrate I, and Ferti-lome Broad Spectrum Insecticide have shown efficacy against CMBS and are more readily available for home gardens, but they're also more harmful to beneficial insects. If used, they should only be applied while crawlers are present.
Horticultural oil products are widely available and have less impact on beneficial insects than bifenthrin and other conventional insecticides with residual activity. They have not been as consistently effective against CMBS as other mentioned treatments but with repeated applications while crawlers are present, they can reduce the population to some extent.
When using any product sprayed onto trunks and branches, be sure to get good coverage, including undersides of branches and bark crevices.
Make sure any insecticide you plan to use is labeled for the type of plant on which you plan to use it, and follow label directions.
Let me know if you have questions.
Contact Mary Helen Ferguson.
Reference to commercial or trade names is made for the reader’s convenience and with the understanding that no discrimination or endorsement of a particular product is intended by LSU or the LSU AgCenter. In some cases, other brands may be available.
Other LSU AgCenter resources:
Avoid bringing CMBS-infested trees into your yard. The infestation on this tree is obvious, due to the sooty mold and the large number of scale insects. However, in the early stages, just a few insects may be present, so look closely. (Photo by M.H. Ferguson)
Crapemyrtle bark scale insects are most susceptible to insecticides sprayed onto the trunks and branches when they're in the first instar nymph (crawler) stage. These are only present at certain times of the year. (Photo: Jim Robbins, Univ. of Ark. CES, Bugwood.org)
