White pine weevils can damage a variety of conifers
White pine weevils (Pissodes strobi) are native tree pests found in Pennsylvania and across much of North America.
Though their common name may give you the impression that these little pests only damage white pines, that isn’t the case. They can also kill the growing tips of other conifers, such as blue spruce, Scots pine, jack pine, Norway spruce, Serbian spruce and Douglas firs.
Identify the weevils
Adult white pine weevils are small and brown with darker brown markings on their wing covers. The snout of these and other weevils is narrow and elongated. The larvae of white pine weevils feeds beneath the bark of affected trees and are grub-like and white with a tan head.
Adult white pine weevils feed on the young, tender growth of host plants, starting in the early spring. They tend to feed on the outermost twelve inches of the stem tips. In April and May, female white pine weevils lay several eggs into each feeding site. Within a week or so, the eggs hatch and the larvae begin to feed as well.
As the larvae feed, they excavate the inner tissue of the stem tips as well as the bark. In late summer, the larvae enter pupation inside of the damaged plant stems. They mature into adults just two weeks later and exit the host plant. For the rest of the summer, the adult weevils do feed on susceptible plants, but the damage they cause in late summer isn’t usually significant. When cold temperatures arrive, the adult beetles nestle down into ground-level debris to overwinter.
Damage, not death
Though there’s only one generation of white pine weevils per year, the damage they cause can make the tree grow in a lopsided fashion. Thankfully, this pest seldom kills the entire plant.
In many cases, when the tree’s leader branch is killed by white pine weevils, a new, lateral branch often takes over as a new leader. You can encourage this by selecting the strongest side shoot to become the new leader. Pinch out the buds of the other remaining side shoots and leave the most vigorous one to take over as the leader.
Young trees are far more susceptible to white pine weevil damage than established trees are. Those trees under 25 feet are most vulnerable. If white pine weevils are present in your trees, you’ll spy dead or dying branch tips that may or may not be curled over.
Get rid of them
As soon as you spot these wilting or dead branch tips, trim them off a few inches below the damage and burn or toss them into the garbage. Doing this before late summer ensures you’re destroying the pest feeding or pupating within the branch.
Beyond carefully removing affected stem tips, there’s one other thing you can do to control this pest without resorting to synthetic chemical pesticides. Since the adult weevils overwinter in leaf litter and crawl up into the trees come spring, apply a band or wrap of waterproof paper or plastic coated in non-drying glue, such as TangleFoot, around the trunk of the tree. As the adult beetles climb the tree, they’ll get stuck in the non-drying glue and won’t be able to access the top of the tree to feed. Leave it in place until mid-summer. And make sure there aren’t any gaps between the wrap and the tree bark that the weevils could sneak through.
There are some systemic pesticides labeled for use against this pest, but I don’t recommend them as they can also be absorbed by surrounding plants and make their way into the pollen and nectar where they could impact pollinators and other beneficial insects.