Two-Lined Chestnut Borer
The Village of Deerfield Public Works Department has been made aware of an insect that is attacking oak trees throughout the Village. The two-lined chestnut borer is a common insect that can cause mortality to oak trees over a few years when the infestation level is high. The insect is usually a pest that attacks oak trees that are already stressed and weakened. Extreme environments such as droughts, storm damage, and weakening from disease are all stresses that predispose trees to two-lined chestnut borer.
What is a Two-lined Chestnut Borer?
A two-lined chestnut borer is a small, native beetle that attacks oak trees and chestnut trees, but occasionally attacks beech trees. They prefer white, black, red, scarlet, bur, and chestnut oaks. They are greenish-black, have an elongated shape and are about 1/5 to 1/2 inch in length. They are usually active between May and July and they emerge from D-shaped exit holes towards the base of the tree. Female beetles lay eggs in the crevices of the bark and when the eggs hatch, they bore their way through the bark and back into the trunk of the tree cutting off the flow of water and nutrients from the roots to the leaves.
How to Identify Two-Lined Chestnut Borer in Oak Trees
Oak trees that are affected by the two-lined chestnut borer show:
- Leaf browning and twig/branch die back.
- D-shaped exit holes measuring 1/8 of an inch wide that are typically found in the bottom 12 to 15 feet of the trunk.
- Branches in the upper canopy that have a wilted look while the bottom canopy is still green.
What can be Done to Help our Oaks?
The good news is that the two-lined chestnut borer is both treatable and preventable. The best defense against two-lined chestnut borer is prevention.
- Ensure oak trees are appropriately watered (approximately one inch of water per week) during dry periods to minimize drought stress.
- Avoid compacting soil, or changing the soil grade or water drainage pattern during construction.
- Avoid damaging the bark.
- Regular pruning and pruning out infested limbs can also help decrease the impact of two-lined chestnut borer.
- Remove and dispose of any two-lined chestnut borer-infested wood before beetles emerge by chipping, burning, or solarization.
- Cover all oak woodpiles with plastic tarps from mid-May to mid-July to limit borer movement. Bury the edges of the tarp to contain the borer
The Village of Deerfield Public Works Department is currently monitoring the oak trees for two-lined chestnut borer and other insects and diseases. Treatment is underway for parkway trees that are symptomatic and we plan on proactively treating public trees in high risk areas.
We recommend that residents contact a certified arborist for treatment options and treatment strategies for battling two-lined chestnut borer. If signs or symptoms of two-lined chestnut borer are present on your trees, injection or soil drenching of insecticide may be needed.
For other questions regarding two-lined chestnut borer, contact the Public Works Department at (847) 317-7245.