White pine weevil (Pissodes strobi) is a native North American insect that attacks native white pine in eastern Canada while in prairie provinces it only attacks spruce trees ( white, Colorado, and Norway). The white pine weevil attack and injure terminal leader of spruce trees. In late June, affected new growth will wilt and turn into “ shepherd’s crook” shape. Needles at the beginning are yellowish but ultimately die turning brown and drop. As results of injuries from weevil, young white spruce trees reduce growth, get stunted and develop bushy appearance with multi-stems terminal leaders. Tree mortality from this white pine weevil is rare.
Weevil attack spruce trees that are less then 30 feet in height and exposed to full sunlight. White spruce trees planted in shelterbelts or small plantations on poor and unproductive sites are the most susceptible to outbreaks. The adult weevil is brown that looks like a beetle except they have a long snout. They are about 8 mm long. White larvae with brown heads grow 10 mm long and are found under the bark of the dying leader. Adult weevils overwinter on forest floor and make short flights early in the spring to disperse. Adults lay their eggs at the tip of the previous year’s leader in May and early June. The white pine weevil prefers to attack trees exposed to direct sunlight.
Symptoms – How to recognize it
The damage is mostly occurring by larvae that feed under the bark of the white spruce terminal leader. Also entering holes made by mature weevil can cause terminal leader to break. By late June these are noticeable symptoms that trees are under the attack of this insect:
- Most of the damage is caused by larvae and in trees less than 6 meters ( 20 feet) in heights
- new leader or top of the tree are showing signs of wilting/drooping and the needles turn yellowish/brown
- infected leader has very characteristic “shepherds crook” shape
- Hole along main stem of the trees
Management- What can you do
There are very few management options for the control of the white pine weevil :
- Early detection is most important to prevent damage from the weevil. As soon as white spruce trees reach one meter (1m) in height you may perform regular check up for this insect.
- Pruning is probably the most effective method once weevil infest your trees. Pruning must be done prior to the beginning of August when larvae are still active in the trees and before emergence of new adult (Aug/Sept).
- Remove “Shepard’s Crook” immediately once you notice it or you notice holes in trunk earlier. Cut should be made back at the level of the topmost whorl of unaffected branches ( where you don’t see any holes on trunk).
- After you made a cut at the branch whorl – you may need to cut additional side branches leaving one to become future leader. This way you will avoid having two leaders on the tree.
- Consider planting non-host species OR planting a deciduous species mixture that will provide shading for the spruce trees.
- There are a very few chemical and biological products to successfully control this insect.
How Can We Help?
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