This insect is becoming a more serious pest to Ash trees in Calgary. Hot weather and a lack of water can cause stress for Green Ash and make them more susceptible to infestation. The Western Ash Bark Beetle lays its eggs in twigs and branches. Larvae develop and start galleries in the stem. As feeding continues the tissue in the stem is cut off from the rest of the tree and the leaves on the tip side of the gallery start to yellow and eventually these branch tips die-off. This insect mainly affect Green Ash (Fraxinus pennsylvanica) in Calgary but can also affect Black Ash (Fraxinus nigra) and Manchurian Ash (Fraxinus mandshurica).
Key Points
- Trees heavily infested with this insect accumulate large quantities of deadwood in the crown.
- Leaves will often wilt and turn bright yellow from the affected part of the branch outward toward the tips.
- Trees that are already affected should be pruned to remove the dead and heavily infested branches. This is effective in helping to control the insect.
Tree Damage
The damage is due to the galleries constructed by the female insect. Leaves will often start to wilt and turn bright yellow from the gallery (point of damage) outward to the end of the branch. A row of holes about 1mm in diameter encircle the branch. These galleries are formed by the hatching insects exiting the affected stems. The ash bark beetle is most prevalent in trees that are already “stressed” by some other factor (Lack of water, poor past pruning etc.). Heavily infested trees accumulate large quantities of deadwood in the crown because insects can repeatedly attack the same tree in successive years. This repeated infestation can have a negative impact on the tree’s health.
Control Measures
- The best control for this insect is prevention by keeping your tree healthy by regularly pruning to remove dead branches and ensuring the tree recieves enough water.
- Trees that are already affected should be pruned to remove the dead and heavily infested branches.
- There is no chemical or spray control available for this insect.
