Dead and Dying Birch Trees (06/20/13)
Dead and Dying Birch Trees
I’ve received several calls and emails recently about birch trees with dead and dying tops. The cause is likely an insect pest called bronze birch borer. Additional signs and symptoms of bronze birch borer are D-shaped exit holes on the branches or stems, just below the dead area, and stems that have a “muscled” appearance (see photos).
Borers are almost always secondary pests, homing in on trees that are stressed. In this case, there is a clear link between drought stress and attack by bronze birch borer, and we’re likely to see an increased incidence of this pest following last year’s drought. Therefore, one of the simplest ways to fight bronze birch borer is to make sure birch trees are well-watered. Trees that receive proper watering are able to fight off this insect and they can even make a full recovery.
Insecticides can be effective, but they are not guaranteed to completely eradicate the pest. The most commonly used systemic insecticide is imidacloprid (many products), normally applied as a soil drench. It can kill borers, if the tree is able to take it up and distribute the chemical throughout the tree.
However, if the tree’s vascular system is compromised too much, it might not be able to take up the chemical from the soil and distribute it. This product should be applied as soon as possible, as uptake is best in the spring.
If the top of the tree is dead, it will have to be pruned out. A side branch will likely take over as a new leader, or the tree may send up a new shoot from the main stem. In either case, the ideal tree form will be lost, though the tree can still be a fine specimen.