Native to North America, damage caused by the BBB 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.

Early symptoms of the BBB include yellow leaves, branch dieback, and an overall thin appearance to the upper part of the canopy. Larvae feed underneath the bark and disrupt the flow of water to the canopy. Wound tissue forms around these disruptions, creating a serpentine lump underneath the bark. Eventually the symptoms progress downward to the lower branches and trunk.

Susceptible Hosts

All species of birch (Betula spp.) may be attacked, but some species are more susceptible than others.

Symptoms

• Small branches in the upper 1/3 of the crown will be thin and begin to die back

• Leaves on infested branches will be stunted, yellow, or show marginal chlorosis in May or June

• Over time dieback continues downward to larger branches

• Infested birch trees typically die in 3-4 years

• D-shape exit holes (flat-headed borer)

• Ridges may appear on the bark of the trunk and larger branches in response to larvae feeding beneath the bark in the phloem tissue

Signs

Insect Adults

• Adult borers are slender, about 3/8 inch (10 mm) long

• metallic-coppery colored beetles (are rarely seen)

Larvae

• Larvae occur underneath the bark and are white, segmented, legless grubs with an enlarged area behind the head • 1/2 inch long when mature

• The larvae of the bronze birch borer generally feed in the phloem tissue, but occasionally bore into the outer sapwood

• Larvae feed laterally around the branch

• Zigzag galleries are often formed

Distinguish from Look-alikes

• Brown leaves are not always associated with the bronze birch borer. Birch leafminer also causes leaves to turn brown.

• Birch trees in typical urban sites frequently develop symptoms related to abiotic stress. Wilting leaves, mineral deficiencies, and decline may be apparent on stressed birch trees regardless of the presence of the bronze birch borer.

The best protection from the 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 preventively 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. Additional protection can be obtained through cover sprays of insecticides to the trunk and main limbs. Trees infested with BBB may be similarly treated, although trees with serious decline are unlikely to be saved.

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