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Be vigilant against pest, crape myrtle bark scale
OCEAN SPRINGS, Miss. -- A new insect pest found in Mississippi on March 15 could take away the crape myrtle’s status as a beautiful and low-maintenance landscape tree.
Crape myrtle bark scale, or CMBS, is an invasive insect that came to the United States from China. It was first found in Texas in 2004 and has since spread east to Shreveport and Houma, Louisiana; Little Rock, Arkansas; and Germantown, Tennessee. Ocean Springs joined this list when the insect was found on the coast in Jackson County.
Gary Bachman, Mississippi State University Extension Service and Mississippi Agricultural and Forestry Experiment Station horticulturist, discovered the insects in Mississippi.
“Crape myrtle bark scale appear as white- or gray-encrusted waxy spots around pruning cuts and in the crotches of branches,” Bachman said. “Underneath the waxy coating, the scale appear to be pink.”
What usually notifies a homeowner of a CMBS infestation is the presence of scaly, flaking patches of black, sooty mold on the tree. This mold is the result of a sticky “honeydew” that drips down from the pests onto anything below.
Blake Layton, Extension entomologist, said the presence of this invasive insect in Mississippi is a significant problem.
“Historically, crape myrtles have been a very beautiful, low-maintenance tree, and this thing has the potential to turn them into an ugly, high-maintenance landscape tree,” Layton said.
Layton recommended that anyone who finds CMBS on their crape myrtles should battle the pest aggressively.
“We don’t know how fast this will spread within a landscape, so the best advice is to treat infested trees aggressively and as soon as it appears,” he said. “When possible, destroying infested plants in a manner that will prevent the spread of scale to nearby crape myrtles may well be the best response. However, this is most practical for small, recently installed plants.”
If an infected crape myrtle cannot be removed, it should be treated with a series of products, including a soil-applied systemic insecticide and supplemental foliar sprays. Layton recommended using a soil-applied insecticide that contains imidacloprid or dinotefuran.
“This treatment should be applied in late spring but before the trees begin to bloom so the chemical does not harm pollinators,” he said. “We recommend doing this in late April to May.”
These treatments can be applied only once a year, but Layton said they give fairly long-term control. While effective, they do not provide 100 percent control.
“You can use a soft-bristle brush with water and dishwashing liquid to scrub the black mold and scale insects off the trunk,” Layton said. “That will improve the looks, but it won’t get rid of the problem because scale will also be on twigs and limbs higher in the tree.”
To supplement the soil-applied systemic treatments, use foliar sprays containing the insecticide acephate or the insect growth regulators pyriproxyfen or buprofezin to control crawlers and newly settled nymphs. Homeowners are encouraged to seek assistance from licensed commercial applicators for treating large trees and to follow label precautions for pollinator protection.
The best approach is to examine trees carefully before buying them or transplanting them into a landscape, and then monitor them afterwards. Nursery trees are inspected by the Mississippi Department of Agriculture and Commerce Bureau of Plant Industry to ensure that healthy, noninfested stocks are available for sale.
“Do your best to make sure you are not buying an infested tree, but this is easier said than done,” Layton said. “A heavily infested tree is easy to spot, but if it’s much harder if it’s lightly infested.”
Experts are trying to track the spread of this new insect pest, so anyone who suspects they have crape myrtle bark scale on their trees is asked to contact the local county Extension office and report their detection.