How do we stop woodworms?

Log home

We are in the process of renovating a cedar log home. The bottom logs were partially rotten, and we replaced them. We have recently found fine sawdust trickling out of holes in some of the other logs higher up, and we think we may have woodworms. How should we treat the wood to stop them? —Sepp Gmeiner, Toronto, Ont.

“Woodworms” is a general term for the larvae of wood-boring beetles that attack pretty much any raw wood: lumber, flooring, furniture, tool handles, picture frames, wooden toys, fishing poles…you get the idea. There are a number of beetles that do this, and they have different life cycles and host preferences.

Before you do anything, ideally you’d know (through expert help) the type of beetle you’re dealing with, and how they got in. For example, were they in the new logs (possible, but not likely) or did they come from infested firewood you brought into the cottage? Also assess the extent of the infestation. There’s no sense in treating every stick of wood in the house if the beetles are confined to a few logs, which could be replaced.

Kathryn Nystrom, an insect identification officer with the Great Lakes Forestry Centre, thinks yours may be powder post beetles, the most widespread wood-boring beetles in Ontario. They attack hardwoods and softwoods, and push a fine, powdery sawdust (called frass) out of their exit holes. Seeing exit holes and frass doesn’t always mean the wood is infested; the beetles might have moved on or died out on their own. Unfortunately, says Nystrom, “if you’re just seeing it for the first time, it’s probably an active infestation.”

Treat the wood with a borate solution, such as Timbor, says Scott McClenaghan of Steve’s Pest Management in Chatham, Ont. It works against wood-destroying insects, plus acts as a fungicide. You can apply it as a liquid, foam, or dust, but the wood needs to stay dry until the product dries.