Crape Myrtle Bark Scale on Crape Myrtle Tree
By Elaine Pugh, Fairfax Master Gardener
Crape myrtle bark scale (CMBS), a type of felt scale, is a serious threat to the crape myrtle, Lagerstroemia indica. The pest has now been found in the Virginia Beach area, and may reach Northern Virginia.
The crape myrtle is a commonly-used flowering, small-leafed, multi-trunked specimen tree or shrub in the South that comes in all sizes and shapes from a large vase-shaped tree to a small shrub. Profuse flowers in the summer are found in various shades of red, pink, white and lavender. The fall colors of yellow, orange or red add color to the landscape. Smooth, exfoliating bark also adds to its beauty in the winter to give it a four-season use in the landscape.
What is this pest?
The technical term for crape myrtle bark scale is Eriococcus lagerstroemiae, a type of invasive felt scale from Asia related to the azalea bark scale and oak eriococcin scale. According to the Mississippi State University Extension Office, adult females produce a white, felt-like sac around their bodies and lay approximately 100 to 300 pink eggs inside this sac. Eggs hatch into tiny pink crawlers, and the older nymphs are pink, gray or brown. Adult males, rarely seen, are winged and mobile. They can complete two to four generations per year in the Southeast. (Texas A&M University shows a chart of the generation cycles.)
Fluffy white and gray, tiny bumps with sooty mold are seen on the bark and twigs. Sooty mold is a black fungus that grows on honeydew, the excrement of aphids and scales. As compared to soft or hard scales, these scales feel like felt when touched. Pink blood-like fluid runs out when scales are crushed.
How does it spread?
Long distance infestation comes from unknowingly planting a purchased infected plant or by improperly removing a plant already infected. Once on a tree, the scale can spread by wind, or by crawlers in contact with birds, flying insects, small animals or people. Heavy infestations may also extend to the leaves and to nearby low-growing plants, grass and mulch. Once in an area, it spreads rapidly from tree to tree, even when trees are hundreds of feet apart.
Where did it come from and how fast is it spreading?
CMBS was first discovered on crape myrtle trees in the United States in the Dallas/Fort Worth area in 2004, probably on an infested nursery stock import, and has been rapidly spreading to cover 13 states. It reached Mississippi in the spring of 2015, North Carolina in August 2016 and Virginia Beach, Virginia in January of 2017.
Does it hurt the tree?
According to the North Carolina Forest Service, CMBS can cause considerable damage to crape myrtle trees, including stunted growth, branch dieback, reduced flowering and limit photosynthesis capabilities. It does not kill the tree, but it is very unattractive and weakens the tree.
How do we get rid of it?
- Inspect plants for felt scale before purchase and avoid it.
- Plant another selection instead.
- Use a systemic soil-applied or foliar insecticide spray for treatment. (Horticultural oils and lady bugs as predators are only mildly effective.)
- Soil-applied Insecticide. Eric Day, the Entomologist for Virginia Tech, recommends the use of the systemic imidacloprid as a form of treatment for homeowners in Virginia. The best time to apply soil-systemic pesticides is after the leaves begin to bud out, and these treatments take several weeks to work.
In other states, the Extension Office of the Mississippi State University recommends soil-applied insecticide crape myrtle bark scale treatments showing charts for both homeowners and professionals. Treatments that have proven most effective for them are the ones that contain active ingredients including very low doses of dinotefuran, imidacloprid, a combination of imidacloprid + clothianodin, or thiamethoxam. (Crawler sprays with insect growth regulators with products containing pyriproxyfen or buprofezin can supplement soil-applied systemic treatments for more aggressive control.) Note that pesticide users are required by law to follow the usage directions on the container.
- Contact Spray. The Texas A&M Extension Service also recommends the option of a contact spray with an insecticide such as bifenthrin. The bark scale are targeted in their immature stage at their peak (later than for systemic pesticides) and then two weeks later to catch those that have emerged following the first treatment. Again, note that pesticide users are required by law to follow the usage directions on the container.
- For either the soil or spray method, the sooty mold will still remain unless removed. Heavier accumulations can be scrubbed off with a soft-bristle brush, water and a bit of dishwashing liquid. Scrubbing the sooty mold before applying the pesticide will make the control more effective. Washing alone will not stop it.
- Remove it. The Extension Office of Mississippi State states that when destroying infested plants or pruned branches, it is important to do so in a manner that will prevent spread of scale to nearby crape myrtles. Burning or placing infested plants in a landfill where they are promptly buried are suggested methods of plant destruction and disposal. Trucks and trailers used to haul away infested plant material must be tightly tarped to prevent wind-blown spread to other crape myrtles located along the route to the disposal site.
Can this be confused with anything else?
The crape myrtle aphid also causes sooty mold, but does not have scales.
CMBS is an invasive pest on crape myrtles that is difficult to control, but early identification and a pro-active plan of attack are key to managing the potential damage. If you suspect that you have this pest, please contact your Virginia Extension Office.
News –- We hate to report that crape myrtle bark scale is here, Oct–Dec. 2016 Newsletter, Virginia Landscape Nursery Association
Crape Myrtle Bark Scale: A New Exotic Pest, Pub. EHT-049 3/14, Texas A&M AgriLife Extension
Crape Myrtle Bark Scale Identification and Control, Pub. 2938 (POD-02-16) Mississippi State University Extension
Crape Myrtle Bark Scale: New Tree Pest Has Arrived in NC, post by Dr. Frank, NC State Extension
New scale insect threatens the South’s beloved crape myrtle, North Carolina Forestry Service
Crape myrtle bark scale study reveals tree treatments to fight pest, Texas A&M University