Bronze Birch Borer (Agrilus Anxius) is a native Wisconsin borer found only in birch trees. BBB will feed on healthy or stressed birch trees introduced from Asia and Europe, but only feed on stressed native white (paper) and grey birches. If you have a river birch you may stop reading now, as they are essentially immune to BBB.
The first symptom of BBB is branch dieback (dead) in the top of the tree. The 1/4-1/2" bronze bug bores into the top of a tree to consume the conductive tissue of the branches. This infestation will result in branch death above the gallery (feeding zone) and if not stopped will work their way down the tree, killing more and more of the tree.
The larvea feed on the conductive tissue of the upper canopy first, once this tissue is destroyed the branch above where they fed dies. The leaves on that branch or branches where the bugs are turn brown and usually stay on the branch. Moving down the infected branch often you can notice the leaves are small or sparse and not very green, sometimes even red or brown. Moving further down the branch towards the trunk the leaves of the infected branches are usually fine, normal size and green. Sometimes you can actually see the ridges from the galleries under the smooth bark. If you observe dead or dying branches in the top of your birch tree please give us a call, we can come out and assess your tree's health.
Stress prevention is your best defense against BBB. A stressed tree loses its ability to move water and carbohydrates throughout the canopy, which lowers its ability to protect against borer infestation.
One of the biggest stressors for birch is planting placement, or where you plant your birch tree. Birch is found in the forest as more of an understory tree, often in partial shade. Their roots are shallow which makes them very suspetible to temperature changes in the soil. Placing a paper birch in full sun surrounded by grass in our climate will not work over time. They really need a bit of shade if possible and big fluffy mulch rings to lower soil temps and increase the water holding capacity of the soil.
Like most/all other trees, drought, soil compaction, root loss, and salt are some of the other major stressors to watch out for. Don't be afraid to water your birch tree, as they may need it more than some of your other trees.