- The locust borer is a black long-horned beetle, referring to its long antennae, with yellow markings on its back. Its legs are reddish in color. However, it is the larvae that are responsible for damage to trees. Larvae are rarely seen, as they live and feed inside the tree. They are white and about ¼-inch wide and 1 inch long.
Signs of Infestation
- The larvae are hatched in the autumn and bore into the inner bark to make a hibernation cell in the tree over winter. Come spring, they bore into the woody part of the tree. The earliest signs of an infestation are what look like wet spots on the bark, caused by the sap oozing from the holes. As the larvae tunnel further into the tree, you'll notice white sawdust either on the tree or around its base. This sawdust will turn yellow as the larvae reach the heartwood of the tree.
- The tunneling significantly weakens the tree, leaving it susceptible to attack from other pests and diseases and also causes significant structural damage. As a result, the tree may begin to drop branches or even break in two at the trunk. Trees that are less than 6 inches in diameter are more susceptible to attack and damage. Larger or more established, healthy trees are less susceptible and more able to withstand an attack.
- Locust trees are typically planted on poor, dry sites because of their ability to thrive in poor soil. However, this makes them more likely to be weakened from drought stress and so more susceptible to a locust borer attack. If you grow a black locust as a shade tree, especially if it's a young tree, be sure to provide supplemental irrigation during periods of drought. The U.S. Forest Service recommends that locust trees be sprayed with either lindane emulsion or carabryl just at bud break.