TWO-LINED CHESTNUT BORER
The two-lined chestnut borer is attacking oaks with increasing frequency. This borer is related to the Emerald Ash Borer and has similar devastating effects on its host. This bug is considered the leading insect cause of oak death and may cause death in just three to four years if not treated.
This borer is usually attracted to stressed oaks, unlike the Emerald ash borer which is aggressive and attacks even healthy ash trees.
But because of the past few hot, dry summers, many oaks are drought-stressed and that is probably why we are seeing more nice oak trees with borer damage.
Healthy oaks that are in close proximity to infested oaks are also at risk of attack.
Infested trees exhibit branch dieback usually starting in the top of the tree, with leaves turning brown and usually staying on the branch for an extended time. The next year, those branches will not have leaves and will be bare. So any oak that has small branch that are browning or bare in the top of the trees or at the ends of branches should be carefully evaluated.
If the dead branches are removed, D-shaped emergence holes may be found in the bark and if the bark is stripped off, galleries (tunnels under the bark) and even live larvae may be found.
Avoid or minimize drought stress by watering during dry, hot weather. A lawn sprinkling system is usually not adequate to give a deep watering to large trees. Running a hose at the base of the tree for 2 to 3 hours a couple times a week may accomplish the goal of deep watering.
Remove infested parts and burn them. Destroy infested oak firewood or strip off the bark to kill any larvae. Cover the woodpile with a tarp if it may contain borers.
Enhance the health of the trees by fertilizing and/or mulching.
The same insecticides that kill Emerald ash borers will be effective for two-lined chestnut borer. TREE-Age, or emamectin benzoate, gives excellent control of this type of borer and one injection gives two years of control.
For prevention in trees not already infested, imidacloprid soil injection or drench, possibly combined with fertilizer, can give some measure of prevention as it does for Bronze Birch Borer.
For high value oaks, we would recommend both the emamection trunk injection every two years and fertilizing with added imidacloprid every two years.
We have been dealing with ash borers for 14 years. We have been treating this borer that attacks oaks for only the past five years, so our experience is less extensive with this bug.
So far Tri-City Tree Doctor has treated outbreaks of 2LCB in Beaverton, Midland, Saginaw, Sanford, Bay City, and Mount Pleasant. United Tree Service has dealt with the insect in Livingston, Genesee and Shiawassee counties. We have found that treatment seems to stabilize the trees and prevent further damage. Our recommendation is to treat at least twice at two year intervals and then observe the trees for any evidence of new damage. Trees can be trimmed of deadwood in the cold months, October to March.