Wood-Boring Beetles in Log Homes

Editor’s Note: This article was reprinted with permission from Pinto & Associates.

Most log home pests infest the wood before construction, shortly after the logs are felled. Flatheaded borers, certain longhorned beetles, and ambrosia beetles deposit eggs in the bark shortly after the tree is cut. Unless the logs are debarked within a few weeks of cutting, the larvae hatch and quickly bore into the wood.

Debarking and seasoning the wood offers some protection against certain borers. But others, like old house borers and anobiid powderpost beetles prefer seasoned wood. Logs that have been treated with wood preservatives are not fully protected either because natural cracking and splitting of drying logs exposes new, untreated wood for attack.

Many of these same "log home" beetles can be found in conventional frame homes. But they have a hard time surviving the milling process when logs are sawed for "stick" home construction.

Anobiid Powderpost Beetles-attack seasoned softwoods and hardwoods. Females prefer to lay eggs in wood that is 2-5 years old. Anobiids show up in early spring in the first year or two after construction. Adults may continue emerging until midsummer, leaving small less than 1/8-inch), round exit holes with fine cream-colored sawdust. Anobiids can reinfest the logs but structural damage is minimal except in the most severe, ongoing infestations.

Bark Beetles - attack newly felled, unseasoned logs, leaving serpentine galleries in the sapwood just under the bark. Emerging adults leave small (1/16 to 1/4-inch) round exit holes in the bark with a powdery frass that looks like salt and pepper.

Old House Borers - attack seasoned soft woods. In log homes, the adult beetles usually emerge in 2-3 years although development can take much longer. Exit holes are medium-sized (about 1/4-inch) and oval. Frass is pow-dery, sometimes with barrel-shaped pellets. Old house borers are longhorned beetles that can reinfest log homes and can do considerable damage.

Flatheaded Borers - attack recently felled softwoods and hardwoods. Development takes two years or more, depending on wood moisture. The adults, which are often metallic in color, emerge in the spring from flattened oval exit holes (1/4 to 1/2-inch) with powdery, pale-colored frass.

Ambrosia Beetles - attack standing, live trees and are found most often in log homes made with freshly cut logs. They tunnel into the wood where they feed on fungi that grow in the galleries. The blue-black stain in the wood and around the small (less than 1/16-inch), The frass is powdery white.

CONTROL OF WOOD BORERS IN LOG HOMES

You have a couple of different options for treating these wood-boring pests. But first, make sure that the infestation is still active. In general, those borers that attack trees while still standing or immediately after logs are cut, will not reinfest the wood in a home. They require a high moisture content and once the wood dries they are not able to complete development. Those beetles that attack seasoned wood (old house borer and anobiid powderpost beetle) are capable of reinfesting.

Look for fresh holes, fresh frass, and adult beetles. A sound amplification device can detect chewing sounds from mature larvae inside the galleries.

In most cases, wood borers in log homes are treated by surface application of a penetrating borate product or by pressure injection of various insecticides, including borates. Some insecticides can be injected directly into galleries or into drilled injection holes. Beetle exit holes should be filled with a hard-setting wood putty before injecting so that the pressurized insecticide does not emerge from the exit holes. (Note: Powderpost beetle infestations are not usually treated by injection because the holes are too many and too tiny to fill.)

Infested log homes can also be fumigated. Removing and replacing infested or damaged logs is also an option. There are log restorers who specialize in this type of work. Applying a polyurethane coating or other finish to the surface of the logs will help prevent reinfestation by those beetles that attack seasoned wood.

The authors are well-known industry consultants and co-owners of Pinto & Associates.