Two Lined Chestnut Borer

The two-lined chestnut borer, Agrilus bilineatus, is an opportunistic insect that attacks weakened oak trees. It is a native beetle known to attack all oak species found in Wisconsin, red oak being its preferred host. When trees and stands are healthy, TLCB confines its attack to low-vigor trees or broken branches. When drought stress, construction and/or defoliation have reduced tree vigor, oaks are predisposed to TLCB attack. Under severe stress conditions, widespread outbreaks of TLCB can occur.

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The best management against TLCB is prevention; keeping trees healthy and vigorous will allow them to fight off invading borers on their own. Do this through proper watering if possible. Also avoid compacting the soil, changing the soil grade or water drainage pattern, damaging the bark, allowing significant amounts of defoliation by insects or anything else that may stress the tree.

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In mid-July, the first visible symptoms of TLCB infestation occur. Infested oaks may be recognized by the sparse, small and discolored foliage, which is followed by the dieback of branches. Leaves of infested branches turn uniformly red-brown. The leaves on non-infested branches remain green. Infested oaks have a distinctive pattern of dead and live leaves on them. Branches in the upper crown are dead and leafless; branches in the middle crown are dying and have red-brown wilted leaves; branches in the lower crown are alive and have green leaves.

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