Image of the City of Regina

Bronze Birch Borer

Characteristics:

  • Larvae: Larvae over winter in the tree. The larvae burrow into birch trees forming twisting tunnels as they feed under the bark. Larvae destroy the tree tissues that carry food from the roots to the tree’s crown. This is the first stage of “Birch Dieback”. If the tree is completely girdled with tunnels, it will die.
  • Adult: Beetles called bronze birch borer emerge from the tree in June from easily seen “D-shaped” holes. Once they appear, the tree is considered in the decline or second stage of “Birch Dieback”.

Identifying infestations:

  • Appearance of Birch Dieback: Birch dieback is a two stage process. First a tree will become stressed as larvae burrow into the birch tree wood. This weakens the tree so it is more vulnerable to other pests. In the second stage, a few leaves at the top of the tree will begin to wilt, then all the leaves on twigs and small branches. The damage will continue to grow until a large branch or two die.

NOTE: If one-third to one-half of the crown is dead, the tree will not recover and should be removed.

IPM Toolkit:

  • Preventive tools:
    • Plant birch trees which are resistant to birch dieback, such as paper birch (Betula papyfifera). Susceptible birch trees include the European White Birch (Betula pendula) and its varieties, especially Cutleaf Weeping Birch.
  • Physical tools:
    • To reduce ensure the tree is not under stress:
    • Maintain soil moisture - apply mulch around the tree and water weekly (2.5 cm)
    • Fertilize every other spring with 20-8-8 min.
    • In August, prune visibly dead wood at the crown of the tree and any dying branches and twigs found a half a metre below the dead wood. Dispose of the diseased wood at the landfill to prevent beetles from returning to the tree.
  • Biological tools:
    • Woodpeckers and some sapsuckers will eat bronze birch borers.
  • Chemical tools: Not applicable