Thanks for the question.

In dealing with any insect infestation, the absolute first step is correct identification of the actual insect. In your case, how do you know for sure powder post beetles are involved rather than, for example, carpenter ants? Ideally if you would be able to send us pictures of the actual insect that may be responsible, that would be fantastic. Please see:

https://apps.extension.umn.edu/garden/diagnose/insect/indoor/beetles/small/powderpostbeetle.html

https://extension.psu.edu/powderpost-beetles

https://extension.umn.edu/insects-infest-homes/carpenter-ants - what-they-eat-104760

I will look forward to hearing back from you as to your thoughts.  In the meantime, look at the following sites regarding powder post beetle treatments:

https://extension.entm.purdue.edu/publications/E-73/E-73.html - :~:text=Wooden items can be cooled,effective powderpost beetle control services.

https://www.borax.com/products/tim-bor

Both Borax and Timbor are commercial names. As Master Gardeners of the University of Minnesota, it is our policy not to comment upon specific commercial products. Both are based upon an octaborate chemical entity so there may not be much difference between the two with respect to effectiveness.

Again, please get back to us why you believe powder post beetles are involved. Thanks for consulting us.

Thanks for getting back to us.

It was good that you sought out the opinion of a pest exterminator. There are over 70 distinct species of powder post beetles. It’s irrelevant as to what specific species is involved in your situation. Treatments are similar for all powder post beetles. Here is a site showing the most common powder post beetle in Minnesota and probably the one visiting you:

https://bugguide.net/node/view/1218587

In early summer, adult beetles lay eggs on the surface of wood in small cavities. These eggs soon hatch as larvae (grubs) and begin to tunnel into the wood. The holes you see in your beams are evidence of this. These grubs over winter in the wood. This offers them sufficient protection to survive the winter. In the spring they undergo pupation to produce adults. These adults emerge from the wood through the tunnels that the larvae had previously made. The fun then starts all over again.

Borate compounds contain disodium octaborate tetrahydrate are often used as preventive treatments against powder post beetles. Borates penetrate the wood and act as a toxicant to the beetles when ingested. This includes either larvae or adults. They can be applied as sprays, foams, or injected directly into the wood. Both Borax and Timbor possess this active ingredient so one would not expect them to differ significantly in effectiveness. Look at the product labels for both products and use the one with which you are most comfortable. These product labels should also contain instructions as to application modes and when they should be done.

Good luck and thanks for using our forum. Please get back to us with any further thoughts or questions.