Treating Air-Dried Wood with Pesticides

Surface-applied pesticides may be dangerous or even illegal, and will probably do no good. Instead, heat-treat wood to kill bugs. February 14, 2006

I have these three beautiful walnut slabs that I am air drying (at about 20% mc) and have noticed small piles of fraff. Some little critter is nibbling holes in the sapwood. The fellow I purchased the slabs from recommended that I use a 1% solution of lindane and paint the sapwood with it. Where can I purchase lindane?

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Lindane is a very dangerous pesticide. It lasts forever. If you put it on wood (which is illegal), the sanding dust will be very dangerous for anyone who breathes it. Further, if the wood is used for a crib and a baby teethes on the crib, big problem. You should never use lindane, let alone use it on wood. Check with your county extension agent for the rules and registration required to use it.

Note that an insecticide applied to wood only protects the outside skin of the wood. The insects are already inside and so surface treatment does little good. If you dry that wood in a kiln ASAP (130 F), your problems for future damage are ended. Sounds like you have the ambrosia beetle.

From contributor F:
Gene is right, stay away from that poison. I made the mistake of complaining to an old farmer I was buying air dried Oregon ash from that I found a few boards that powder post beetles were in. When I bought more ash from him, the boards stank of the poison (lindane) he had sprayed them with. A safer treatment is simple Borax. Also note that the bugs won't be able to eat the heartwood on the walnut.

From the original questioner:
Thank you for the responses. The slabs are almost 20' long, 60" wide, 13/4" thick. A bit big for kiln drying? I want the natural edge to chip carve and would like some of it to remain in tact and not full of holes. I was hoping to find an easier solution then cooking them in a kiln. Moving them into and out of and to and from my shop is a bit of a job... Each slab weighs about 800lbs. Could you elaborate on borax?

From contributor F:
I haven't done the process myself, but the jist of it is to take the chemical borax and put it in a solution with water and spray it on the wood. I can't be specific on the exact mixture. Again, I want to point out that if you do not intend to use the sapwood portion of the walnut, you can let the bugs be, because they are unable to eat the heartwood.

From the original questioner:
I would like to use the natural edge for this set of office furniture I've designed, so I will try the borax solution. Also recommended was a fully saturated solution of boric acid. I will post results. Maybe I will try both and see if one works better.

From Gene Wengert, forum technical advisor:
At 20% MC, you will not have any new insects getting into the wood, except the lyctid powder post beetle and that comes from infected wood, so you probably have no risk as you have none of that infected wood around.

Any insects in the wood will not be affected by putting a solution of borax on the wood and treating the surface. Borax is intended for green wood, not 20% MC. As mentioned, you will not affect the insects inside the wood, so borax is a waste of time at this point, especially if you want to control the ones that are nibbling already. You cannot rewet the sapwood enough to get the borax inside the wood and not harm the wood.

Further, rewetting dry wood like you have will cause the surface to swell rapidly and can actually pull the inside apart (creating honeycomb). Therefore, one of the primary rules for drying is never rewet partially dried lumber.

As you are going to use the raw edges, I wonder if residual borax in the wood would affect the finishing. Unlike other approved insecticides used on wood when the wood is green, borax lasts for a very long time. I also wonder if borax will discolor the walnut wood.

To heat the wood to 130 F and destroy the insects would be fairly easy. Rent a trailer or a small truck with a separate cargo area, and put the wood inside. Then get a heater and heat the wood to 130. Of course, fire issues mean you will have to be very careful with the heater... maybe keep the heater outside and just push the heated air into the chamber. Think about the safety issues carefully ahead of time.

From the original questioner:
Gene, you are a wealth of information. Thank you for your thoughtful reply. I will follow your advice and pursue the nibblers with heat... the last few days with the Santa Anna winds have felt almost that hot.