Poplar Borer
Saperda calcarata
A large long-horned beetle whose grubs tunnel in the trunks and large limbs of aspen, poplar, cottonwood, and willow, weakening the wood and opening it to decay and breakage. It is one of the most damaging borers of aspen and poplar in much of North America, and repeated attacks can deform or kill a tree over several years.
🔎 How to spot it
The adult is a stout beetle three quarters of an inch to over an inch long, gray to gray-blue and dusted with fine yellowish and brown markings, with antennae about as long as the body. The grub is a legless, cream to pale-yellow larva that grows to more than an inch long and tunnels in the wood. The clearest signs are on the tree: wet, dark stains on the bark and coarse, sawdust-like frass piling up in bark crevices and at the base of the trunk.
🥀 Damage it causes
The grubs bore wide galleries into the sapwood, and into the deeper wood in heavy attacks, scarring and girdling the trunk, slowing growth, and leaving holes that ooze sap and stain the bark dark below the attack. The tunnels weaken the wood so limbs and tops break in wind, and the wounds let in decay fungi that hollow the tree. Because the larvae take two to three years to mature, a tree can carry several broods at once and decline steadily.
🛡️ Prevent it
Keep trees vigorous, since healthy, well-watered trees resist attack far better than drought-stressed or wounded ones; water aspen and poplar during dry spells and avoid injuring the trunk with mowers and trimmers. Planting aspen in groups so the trunks shade one another reduces egg-laying on sun-exposed bark. Prune out and destroy badly infested limbs, and remove severely damaged trees that serve as a beetle source.
🧯 If it is already here
There is no easy cure once grubs are deep in the wood; on a valued tree, individual larvae can sometimes be killed by probing their tunnels with a wire or injecting beneficial nematodes into the holes. Bark sprays of a labeled insecticide timed to the summer egg-laying period can protect the trunk, but the most reliable long-term answer is vigor and removing brood trees. Heavily riddled, hazardous trees should be taken down.
💡 Good to know
Poplar borer is largely a pest of stressed trees, so the outbreaks that follow drought or transplant shock are a sign to improve care rather than only to spray. The combination of dark bark stains and coarse frass at the trunk base is the field mark that separates it from shallow bark feeders. Aspen and poplar are short-lived to begin with, and chronic borer damage shortens their lives further.
🌱 Plants it attacks
4 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.