Boring Bugs on Oak Trees

Identification

• Oak trees are susceptible to serious damage from the goldspotted oak borer (Agrilus auroguttatus), a native pest of Southern Arizona. A number of species of roundheaded borers, the larvae of longhorned beetle, are also likely pests of oak. These include red oak borer and white oak borer.

Description

• The goldspotted oak borer adults are about ½ inch long and have bullet shaped bodies. The black colored moths have gold spots on their forewings. The tiny eggs are laid within the cracks on the bark and branches of larger oak trees. The larvae is 0.8-inch-long, legless and white with a pair of pincherlike spines at the base of the abdomen. Brown to black colored adult longhorned beetles have 11-segmented antennae that are longer than the body. There are small spines on the wings and thorax. The larvae or the roundheaded borers are cylindrical shaped with large mandibles. The gray, brown or black pests have a distinctly enlarged thorax right behind the head.

Damage

• The larvae of the goldspotted oak borer feed under the bark of the oak trees and damage the cambium layer, the main water and nutrient conducting tissues of the tree. Continual injury from pest is likely to kill trees. Early symptoms include sudden twig dieback, thinning crown and gradual decline in tree health. Roundheaded borers create long holes in the sapwood with their feeding, rendering the trees useless for commercial purposes. The adults mainly feed on flower pollen and do not damage trees.

Control

• There are few effective treatment options once trees are infested with the goldspotted borer. The best option is to implement effective prevention strategies which include treating trees every year with bifenthrin or carbaryl. Avoid moving infested wood as firewood to healthy oak growing regions. In order to prevent damage from roundheaded borers, keep trees in good health with adequate watering and fertilizing as vigorously growing trees are less likely to be infested. Remove bark from logs to reduce chances of infestation. The application of pesticides to the bark is not effective after infestation has occurred.