Two-Lined Chestnut Borer

Scientific Name: Agrilus bilineatus

Two-Lined Chestnut Borer is a native beetle that attacks oak trees throughout Minnesota. It is particularly damaging to trees during/after drought periods when populations of the beetles can kill up to 65% of red oaks in forest stands. The best prevention is to reduce the impact of drought or other root stress from occurring to trees in urban landscapes.

Attacks: All Oak species, prefers red and pin oak. Stressed trees are more attractive to borers.

What you will see:

• Infestation first becomes visible in mid-July
• Sparse, small and discolored foliage
  • Dieback of branches follows
• Leaves of infested branches turn uniformly red-brown
• Distinctive pattern of dead and living leaves
  • Branches in the upper crown are dead and leafless
  • Branches in the middle crown are dying and have red-brown wilted leaves
  • Branches in the lower crown are alive and have green leaves
• Larvae create meandering galleries underneath the bark

Life cycle:

• Adult beetles lay eggs on stressed oaks in late May and June
• Larvae feed on the inner bark of live branches and stems
• Larvae pupate under the bark where they over-winter
• Adults emerge through D-shaped exit holes in the bark the following May and June

Cultural Management of Two-Lined Chestnut Borer

Cultural practices:

• Healthy trees are less attractive and more resistant
• Promote sustainable growth
  • Water tree 2-3” per week during summer
  • Water 3-4” per week during drought conditions
  • Do not fertilize without increasing water
  • Provide root enhancement system
• Avoid construction damage
  • Compacting the soil
  • Change of soil grade or water drainage
  • Damaging the bark

Chemical practices:

• Two-lined chestnut borer is susceptible to systemic and topical insecticides

An integrated approach

When caring for urban trees it is important to make a complete evaluation of all environmental conditions to accurately diagnose all stress factors and prescribe care based on specific circumstances. This prescriptive care will help your tree meet its full potential.