Twolined Chestnut Borer

twolined chestnut borerOaks are the primary hosts of the twolined chestnut borer. Some of the more frequently attacked species include red, white, and bur oak, scarlet, pin, and black oak, chestnut, post and live oak.

Adult twolined chestnut borers primarily attack and kill oaks that are damaged by drought, flooding, construction, or trees that are suppressed or declining. Urban oaks that suffer stress from trunk and root injury, soil compaction, and changes in soil depth are equally vulnerable to attack by this pest. Oaks that have been defoliated by insects such as gypsy moth or fall cankerworm are also attacked by the twolined chestnut borer.

The first symptom of borer attack is usually wilted foliage appearing on scattered branches during late summer. The foliage on infested branches wilts prematurely, turns brown, but remains attached to the branches for several weeks or months before dropping. Such branches will die and produce no foliage in the next year. Trees can be killed in the first year of attack; however, death usually occurs after 2 to 3 successive years of borer infestation. Infestations normally begin in the upper branches and work their way down into the main trunk during successive years. Infection by the oak wilt fungus causes similar symptoms in the tree crown, but the foliage wilts, turns brown, and drops from the branches quickly during early summer.

The twolined chestnut borer leaves a permanent visible record of its visit. As adult borers emerge from the host tree, they bore distinctive D-shaped exit holes 1/5 inch wide in the bark. Larvae damage host trees by feeding on the phloem (the inner bark), the cambium (the growth layer producing both phloem and xylem), and the xylem (outer sapwood). Larvae construct galleries of sufficient depth to cut the flow of food and water.

Contact your local certified Davey arborist to learn more about how cultural controls and systemic soil treatments can be used to protect high-value shade and ornamental trees.

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