In Calgary, young spruce trees are the typical host for the white pine weevil. This weevil is a small brown beetle with a long ‘snout‘. Although the adult beetle is seldom noticed, the effects of the grubs, feeding at the tops of spruce becomes apparent in mid-summer as the leader dies.
Key Points
- Damage usually shows up in late July/early August
- Mainly trees under 30 feet tall are infested
- Usually pruning the damaged potion is the easiest control
Tree Damage
The damage to spruce is caused by feeding of the grubs of the weevil inside the developing spruce leader (the top shoot). The female lays eggs in wounds on the leader of spruce in spring, and the grubs spend all summer eating the tissues within the shoot. The leader eventually dies, and then curls over like a shepherd’s crook and turns brown. A close inspection reveals small boreholes at the base of the damage and white sap droplets.
Young spruce, less than 20 feet tall are most commonly attacked. Mature spruce are less likely to be targeted since the beetle does not fly well and usually prefers to climb its host rather then fly.
Damage is mostly cosmetic, and with proper pruning the tree will outgrow the damage.
Control Measures
- Remove damaged leaders by cutting it off well below the grub’s tunnelling.
- If available, select a young flexible side shoot and gently bend it vertically and splint it in place to encourage it to become the new leader. Alternatively, in the year following leader removal, select a new shoot that looks like the best new leader and shorten the remainder so they do not compete.
- There is no chemical or spray control available for this insect.
