About a decade after being first spotted in Texas, an imported pest of crape myrtles has been found in Arkansas, extension entomologists for the University of Arkansas System Division of Agriculture said.
An import from Asia, the crape myrtle bark scale insect lives off plant sap. In large enough numbers, they can be fatal to the plant.
In 2004, they were first spotted in suburbs north of Dallas.
“Since being spotted in McKinney, Texas, in 2005 -- a city that bills itself as ‘America’s Crape Myrtle City’ -- the crape myrtle bark scale has been spreading at an alarming rate,” said Jim Robbins, professor and extension horticulture specialist-Ornamentals, for the Division of Agriculture. “In 2012, it was spotted in northern Louisiana in Shreveport and last year in Houma, in the southern part of the state.”
The insect has also been confirmed in the Memphis, Tenn., area in Germantown.
Robbins said there’s heightened concern about the spread of this insect, considering the popularity of crape myrtles in landscapes across the U.S. Researchers in Arkansas and Texas are working to determine what cultivars might be vulnerable to this insect, and find solid control methods.
Fortunately, crape myrtle bark scale is easy to identify, since it’s the first and only known bark scale to occur on crape myrtles. Adult females look like white or gray felt encrustations and each is about 2 mm in length. Under the gray felt covers, gardeners may discover dozens of pink eggs or crawlers.
“Based on our experience so far, this insect is not going to be easy to control,” said John Hopkins, extension urban entomologist for the University of Arkansas System Division of Agriculture. Current best practices include:
-- For heavily infested plants wash the trunk and reachable limbs with a soft brush and mild solution of dishwashing soap. This will remove many of the female scales and egg masses and make insecticide control more effective. Also, washing will remove much of the black mold that builds up on the bark on infested trees.
-- Horticultural oil has not yet been shown to be effective against this insect, however a winter application of dormant oil to the bark and crotches of the plants where scales shelter may be beneficial. Be sure to use sufficient volume to allow for penetration behind loose bark and into cracks and crevices. Winter is an especially good time to treat for scales because a higher -- winter -- application rate can be used without damaging the plant. Thorough coverage of the tree is especially important when treating with oil.
-- Application of systemic insecticides as a drench applied to the root zone has shown the most promise in tests to date. Imidacloprid, available as Merit® or Bayer Advanced™ Garden Tree and Shrub Insect Control; thiamethoxam, known as Meridian®, and dinotefuran, known as Greenlight Tree and Shrub Insect Control with Safari; have shown best control when applied between May and July. When drenching the soil with a systemic insecticide, allow several weeks for the product to be distributed throughout the plant. Additionally, acetamiprid and clothianidin, also neonicotinoids, have demonstrated good control.
-- Certain insect growth regulators are recommended for scale control in woody ornamentals but haven’t been evaluated on the crape myrtle bark scale.
-- Lady beetles should be protected as the twice-stabbed lady beetle is an efficient predator of this scale.
Both Robbins and Hopkins advise notifying your location Cooperative Extension Service office or state Plant Board if you notice symptoms of scale insect infestation on your crape myrtles in Arkansas.
Robbins, Hopkins and Mike Merchant, professor and extension urban entomologist for Texas A&M AgriLife Extension Service, will have a fact sheet available in February on the pest called “Crapemyrtle Bark Scale: a new insect pest.” Ask your county extension office for FSA7086 or find it online at www.uaex.edu.
The crape myrtle bark scale insect has been discovered in Arkansas in January 2014. It was first reported in the U.S. in the Dallas area in 2004.