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The second year of survey data tracking crape myrtle bark scale has provided researchers information they believe will help mitigate the pest’s effect on trees, said a Texas A&M AgriLife Extension Service expert.

Erfan Vafaie, a AgriLife Extension entomologist and integrated pest management program specialist, and other Texas Extension collaborators in College Station, Huntsville and Dallas, have monitored pest numbers the past two years to help determine crape myrtle bark scale’s seasonal life cycle and peak crawler activity. The data collected has helped researchers develop strategies against them.

The crape myrtle bark scale, an invasive insect species from Asia, secrete a sugary solution, known as honeydew, that subsequently results in black mold along the branches and tree trunk, Vafaie says. The crape myrtle bark scale has not shown to be fatal for plants.

Crape myrtle bark scale on an infested tree in Shreveport, La.
Allen Owings, LSU;

But the bark scale do affect the aesthetics for the popular ornamental tree, especially in the Southern U.S., Vafaie says. Observations suggest the crape myrtle bark scale could be responsible for stunted growth in plants as well as reduced flowering.

Two years of data collected by Vafaie and his collaborators show bark scale crawler, or nymph, numbers peak between mid-April and the beginning of May. He suggests two treatment options – contact spray or systemic – for landscapers or growers who have identified signs of crape myrtle bark scale based on data.

Trees can be treated with a contact insecticide spray as pest numbers peak, followed by another treatment two weeks later, he says. Insecticides with the active ingredient Bifenthrin have proved to work best during the study.

“Separate treatments in two-week intervals are good because you want to target bark scale in their immature stage,” he says. “You hit them during the peak and then two weeks later to catch those that have emerged following the first treatment.”

Erfan Vafaie, Texas A&M AgriLife Extension Service entomologist, Overton, checks crape myrtle trees in downtown Tyler for signs of crape myrtle bark scale.
Adam Russell, Texas A&AM AgriLife Extension service

Vafaie says systemic treatments should be applied much earlier to allow the trees to uptake the insecticide for effectiveness. The best time to apply systemic pesticides is mid-March to the end of March, after leaves begin to bud out and trees are actively taking up nutrients from the ground.

“You want to have a systemic like imidacloprid or dinotefuran that will be taken up into the plant so that by mid-April to the beginning of May it will be present higher in the tree when the bark scale are feeding,” he says. “That way it will target them and kill them.”

Some growers have used dinotefuran as a bark spray, as described on the label, because “drenching each pot individually can prove less feasible in a production setting,” he adds. “We will be trying several more potential treatments this summer to provide more recommendations for growers.”

For more: Erfan Vafaie, erfan.vafaie@ag.tamu.edu