Twig Girdlers

Posted by & filed under Don Buma Blog, Horticulture News.

About this time of year you will begin to see damage from twig girdlers.  Oak is usually the primary host although other trees include elm, linden, hackberry, apple, pecan, persimmon, poplar, sour gum, honey locust, dogwood and some flowering fruit trees.  There will be fallen twigs, sometimes up to 3 feet long. The most likely culprit is the beetle Oncideres cingulata. This insect is distributed throughout the eastern United States from New England to Florida and even as far west as Arizona. This is a long-horned beetle with grayish-brown, stout, cylindrical body. The light brown to brownish-gray larvae, which can be up to an inch long, are also cylindrical with small heads and shiny exteriors.

The female deposits eggs in small scars chewed through the bark late in the growing season.  She then chews a continuous notch around the twig, below where the egg has been deposited, girdling it. This is done because the larva is apparently unable to complete development in the presence of large amounts of sap.

Girdled twigs, which look like a beaver has chewed on them, only in miniature, can remain on trees for a period of time often coming down during a windstorm.  While a large infestation may look unsightly and reduce the vigor of the tree somewhat, the overall effect on the tree’s health is not severe.

Eggs hatch and the larvae begin feeding on dead wood inside the twigs the following spring and continue through most of the summer. They pupate inside the feeding cavity and development is completed during August when the adult emerges to repeat the cycle.

Chemical control is impractical, so it is best to gather and dispose of fallen twigs to destroy the larvae inside. The good news is that natural mortality is often high because fallen twigs are excessively dry or have too many larvae per twig for them all to survive.

For additional information and also information about a similar type damage produced by the twig pruner read this publication from the Virginia Tech Cooperative Extension.