Being a gardener in Florida is exciting. We have many plants to choose from and the weather is mostly pleasant but always seeming to surprise us. One disadvantage of living in such a place, in addition to having so many growing zones, landscape nurseries, and major shipping ports, is that invasive species that land in Florida don’t like to leave. One newcomer in the lineup of invasive pests is the crape myrtle bark scale (Acanthococcuslagerstroemiae). This invasive insect pest made its way from Texas and, as of a few weeks ago, the only Florida sighting had been in Santa Rosa County. Unfortunately, this pest has now been confirmed in Leon County. Landscapers and gardeners in north Florida should learn how to identify this pest and what options are available for control.
The crape myrtle bark scale, as the name suggests, has a pretty specific host – the crape myrtle (Lagerstroemia spp.). However, in the United States, this scale has also been found feeding on our native beautyberry (Callicarpa americana). Due to the widespread planting of crape myrtles, these should be the gardeners primary focus when looking for this new pest. If present on the tree, it is hard to miss. These scales feed on the bark and are a snow-white color. Being a scale, they produce honeydew that is then covered in black sooty mold. So, if you see a crape myrtle with black branches, look closely and you may see the white scales. If you crush these scales and they leave a pink goo on your fingers, then you very likely have crape myrtle bark scale. Of course, you can send a picture or sample to your local county extension office for confirmation.
Black sooty mold and white scales along the trunk and branches are a tell-tale sign of crape myrtle bark scale. Credit: Mark Tancig, UF/IFAS.
If you do happen to find crape myrtle bark scale in your own landscape, or one that you manage, proper control is important to prevent it from moving along any further. Since scales suck on sap and are protected by an outer shell, systemic insecticides are the preferred product for effective control. These include the neonicotinoids, such as imidacloprid (Merit) and dinotefuran (Safari). The larval stage can be controlled with a horticultural oil, sometimes mixed with another insecticide like bifenthrin (Talstar), however, this will not control the adults. Another option is to completely remove the tree and burn all of the plant material.
Excessive sooty mold has turned these branches black. Be on the lookout for crape myrtles looking like this to help identify crape myrtle bark scale. Credit: Jim Robbins, Univ. of Ark. CES. Retrieved from bugwood.
The crape myrtle bark scale can significantly reduce the aesthetic value of crape myrtles due to the black sooty mold that covers the bark. It is also known to reduce flowering and can lead to thinning of leaves. Since crape myrtles make up a big part of our managed landscapes, let’s all work together to scout for this pest and control it when found. If you have questions, please contact your local county extension office.
Difference in flowering due to crape myrtle bark scale damage. Credit: Jim Robbins, Univ. of Ark. CES. Retrieved from bugwood.
Crapemyrtle bark scale are often found in branch crotches and wounds to the bark. Photo credit: Gary Knox, UF/IFAS.
There is a new pest in the western panhandle of Florida. Crapemyrtle bark scale (CMBS) is a scale that is found on the trunks, branches, and twigs of crapemyrtle. It is the only known scale insect found on the bark of crapemyrtle. There are other scales that occur on the leaves.
When scouting for this pest, look for very small (2 mm or 0.08 inch) white or light gray spots on the bark of crapemyrtle. The adult females do not ever move once they have found a place to feed and reproduce. Under her protective covering, she lays eggs that hatch into ‘crawlers’ that then crawl away to find their own spot to settle down. When squished, they exude a pink goo (the eggs or newly hatched crawlers). Males are winged and travel to find their mates. See this comprehensive information on their interesting biology.
While the scale does not outright kill the trees, it lessens their landscape value and can reduce flowering. And like other scale, CMBS secretes lots of honeydew; black sooty mold then feeds and grows on the honeydew. The black sooty mold does not harm the plants directly, but it is unsightly and can interfere with photosynthesis if present on the leaves.
Crapemyrtle bark scale are white to gray and ooze pink when squished. Photo credit: Gary Knox, UF/IFAS. ,
Unfortunately, CMBS has also been found on a very popular native bush, American beautyberry, Callicarpa americana, and it is yet unknown whether CMBS will expand its host range to other plant species in our country. In Asia, this pest has been found on some economically important crops like pomegranate and persimmon.
CMBS is a tough insect to control. And it is best left to the professionals. Dr. Adam Dale, an entomologist at the University of Florida, recommends using pyriproxyfen (in the product Distance) or buprofezin (in the product Talus). These are insect growth regulators that have shown to provide great control of CMBS and other similar scale insects on trees and other woody plants. Although these products are not systemic, they are translaminar, which helps increase their control and reduce any non-target effects on beneficial insects like bees. Two applications 7–14 days apart are suggested. However, these products can only be applied by licensed pest control applicators.
Severe infestation of crapemyrtle bark scale and sooty black mold. Photo credit: Gary Knox, UF/IFAS.
Systemic insecticide drenches are effective but pose a dangerous hazard to bees and other pollinators as the poison also gets into the flower nectar. The product labels prohibit application of these type of products to flowering plants for that very reason.
Routine close inspection of your crapemyrtle trees is critical for CMBS control. Early treatment will help prevent heavy infestations as seen in some of the photographs. When pruning your crapemyrtles, thoroughly clean your tools between plants to prevent any accidental spread.
Prevent this scale from coming into your landscape in the first place. Inspect all new plants you are considering adding to your landscape for any sign of CMBS or other insect or disease presence.
This pest has made a home in numerous counties scattered throughout the southeastern U.S. and has a moderate to high probability of becoming a problem in Florida. Follow the link above to learn more about this probable pest.
Life cycle of the crapemyrtle bark scale. Nymphs that hatch from the eggs (a) are highly mobile and are called “crawlers” (b). Some nymphs form a white sac and develop into prepupa (c) and then to pupa further inside, before becoming an alate male (e). The females (d-f) do not enter the pre-pupal stage, and start producing eggs following mating with the male. Life cycle by April Martin and Xavier Martini, University of Florida.
