Bronze Birch Borer
Native to North America, damage caused by the Bronze Birch Borer (BBB), Agrilus anxius, dates back to the late 1800’s and continues to present day. This pest is known to attack all native and non-native species of birch, although susceptibility varies. The BBB is opportunistic and thrives in birch trees that are weakened or stressed by agents such as drought, soil compaction, root injury, other insects, and old age. Birch trees tend to prefer cool and moist growing sites, which are not typically found in most residential and urban areas. With frequent stress caused by dehydration, high temperatures, and compacted soils, landscape birch trees are commonly attacked by this pest.
Trees at Risk
All species of birch may be attacked, but some species are more susceptible than others. Among the most susceptible are whitebarked Himalayan birch, European white birch, European white weeping birch, yellow birch, sweet birch, paper birch, whitespire birch and grey birch.
The best protection from the bronze birch borer (BBB) is prevention. Because this pest attacks weakened and stressed trees, care and attention should be given to maintaining tree health by watering during drought, mulching, and minimizing damage to the root zone that could cause root injury and stress. For new plantings, consider other species that are more stress tolerant.
As a rule of thumb, if more than a third of the tree is infested the chances of saving it are significantly reduced. Infested branches and deadwood should be removed, so give attention to what the tree will look like before deciding on subsequent treatments.
High value trees at risk for infestation by the BBB may be treated preventatively with Xytect™ insecticide. A soil drench in the fall or early spring will provide season-long protection. Xytect™ will also provide protection from the birch leaf miner, which causes additional stress by feeding in leaves. Trees infested with BBB may be similarly treated, although trees with serious decline are unlikely to be saved.
Emamectin benzoate† can also be used at a rate of 10ml/DBH” during the growing season. This treatment is good for 2 years.
†Tree injection treatments recommended if soil applications are not feasible.