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DescriptionBronze Birch Borer

Bronze birch borer (Agrilus anxius Gory) larvae are flattened, creamy-white, legless grubs with light brown heads. Adults are slender, olive-green to black beetles with metallic bronze reflections.

Plants Affected

This native beetle attacks both native white birch and European weeping birch. While its typical host tree would be mature birch trees 40 years or older, it will attack even young birch trees when population outbreaks occur.

Such an outbreak was triggered in Grande Prairie in the early 2000s by the onset of a drought cycle. The outbreak has not yet ended.

European cutleaf weeping birch have no resistance to this pest and are not recommended for planting in Grande Prairie.  Paper birch, which evolved with the borer, have the ability to increase their sap pressure to push the beetle larvae out, so long as they remain well-watered.  Unfortunately, due to the drought cycles that Grande Prairie experiences on a regular basis, the trees lose their ability to fend off the beetle and eventually die from its attacks as well. 

Symptoms

  • Dead limbs at the top of the tree.
  • D-shaped bore holes are visible below dead limbs. Bronze Birch Borer
  • Successive years of attack progress down the tree until it dies.

Controls

  • Ensure your birch trees are well watered during dry periods.
  • Leave low branches in place to keep the tree's shallow roots cool.
  • Don’t dig in the root zone.
  • As soon as damage is observed in the top limbs of the tree, prune out all deadwood at least 12 inches (30cm) below the lowest bore holes to ensure all beetles are removed.  Burn or chip the wood immediately.
  • Do not plant susceptible birch species such as paper birch or European cutleaf weeping birch.  The river birch (Betula nigra) has darker tan bark and is considered resistant to bronze birch borer. 

Bronze Birch Borer     Bronze Birch Borer

Last updated: 7/5/2018 10:49:20 AM