Crape myrtle bark scale continues to spread
Crape myrtle bark scale on an infested tree in Shreveport.
--Allen Owings photo
BATON ROUGE — A new invasive scale insect continues to infest crape myrtles in Texas, Louisiana and other south-central states.
The insect was first identified in the United States in the northern metroplex of Dallas in 2004 and has spread from there, according to experts.
Crape myrtle bark scale has been found in Texas, Oklahoma, Louisiana, Arkansas, Tennessee and Georgia. Land-grant university faculty at Texas A&M University, the University of Arkansas, Mississippi State University, Auburn University, the University of Florida and the University of Georgia are currently scouting for this invasive pest and working on control recommendations and biology.
“Ground-zero for crape myrtle bark scale in Louisiana is the Shreveport and Bossier City areas,” said LSU AgCenter horticulturist Allen Owings.
Crape myrtle bark scale has also been found in Minden, Rayville and Monroe, but it had earlier been found in Houma. A new possible infestation is in Alexandria.
“There is concern that crape myrtle bark scale is also at other locations in the state,” Owings said.
This insect was first brought to the attention of LSU AgCenter forestry agent Ricky Kilpatrick over two years ago by arborists in the Shreveport area.
“The problem with these invasive species is we don’t know the extent of damage they produce,” said LSU AgCenter entomologist Dennis Ring. He suspects the insect is being spread by human activity — such as by infested pruning equipment and by moving plants having scale.
Another problem that allows the insect to spread uncontrolled is many people may have it on their plants and don’t know it, Owings said.
“Because control is not attempted, the pest continues to multiply in numbers and spreads,” he said.
The scale excretes honeydew that coats leaves and limbs. The sooty mold is typically in much higher concentrations than with an aphid or white fly infestation.
“There is still no documented evidence on how the crape myrtle bark scale arrived in the United States,” Owings said. It is known to have been China prior to being in the United States.
People are beginning to see the insect in high numbers, and they want to know what it is and what they can do about it, he said.
Treatment includes using a systemic insecticide in mid-spring, and populations will accelerate through the year without spring control.
Dormant and/or horticultural oils do not seem to offer much control, the experts say. But some people have been successful in pressure washing trees to physically remove the scale.
The scale also seems to have good over-wintering capacity. “Many trees with high infestations last fall have higher infestations this year, even after our colder-than-normal winter this past year,” Owings said.
AgCenter experts are asking people who find this scale on their trees to take a sample a LSU AgCenter office in their area or contact a local AgCenter agent to begin the process of proper identification.