Twig Girdler: The possible culprit for trees losing twigs

Twigs up to three-feet long are falling now from such trees as the apple, dogwood, elm, honey locust, hackberry, linden, oak, pecan and poplar.

The downed twigs look as if a miniature beaver has chewed them off. But the real culprit is a long-horned, gray-brown, barrel-shaped beetle that's popularly known as the twig girdler (Oncideres cingulata), said Ward Upham, horticulturist with Kansas State University Research and Extension. The larva are also cylindrical with a small head and shiny integument. Larvae can be up to one-inch in length and are light brown to brownish-gray.

We most often see twig girdler damage from August to September. It is relatively easy to tell the difference between twig girdler damage and squirrel damage as squirrel damage is more tattered and cut at an angle.

"The female beetles cut small slits and deposit their eggs under the bark. Then, they cut a V-notch around the entire twig -- apparently because their larvae won't be able to complete development if they're around lots of sap," Upham said. "This notch destroys the twig's vascular system, but leaves its central core."

As a result, the branch slowly dies and becomes brittle, he said. Then the wind snaps it off. So, when the twig drops, its separation point has a smooth outside cut, but a ragged core.

Next spring, the eggs will hatch, and larvae will begin feeding on the dead wood inside the twigs. The insects will pupate there, too, and next year's adults will emerge in August.

"Although the adults feed on the bark of host twigs, their damage is minimal until the females start girdling. Then large infestations can result in a high percentage of girdled twigs -- which may reduce the vigor and appearance of the tree," Upham said. "Still, the overall effect on tree health isn't severe."

"The real problems are: The twigs are unsightly. They don't fall all at once, so clean-up is a drawn out process. And, chemical control of these pests is impractical, so you need to gather and dispose of the fallen twigs by spring, to get rid of next year's larvae."

More information on the twig girdler or other tree insects is available in the Extension Office.

Editor's Note: Delta George is a K -State Research and Extension agriculture and 4-H extension agent assigned to Bourbon County. She may be reached at (620) 223-3720.