Bug Control in Ash and Oak

Details about the heat conditions required to kill insects in a load of lumber being kiln-dried. March 28, 2012

I am having a problem with small black bugs boring in my ash and white oak kiln dried lumber. I have put the (packaged) lumber back in the kilns to try and kill them, but am not having success. I've been leaving it in at 100-120 degrees for about a week. Do I need to go hotter or longer in the kiln?

Forum Responses
(Sawing and Drying Forum)
From contributor I:
You need to get the wood to 133 degrees.

From contributor R:
Make sure the core is 133F.

From contributor D:
It's heat plus time. I think I read somewhere 160 F for 3 hours, or 145 F for 24 hours to kill all ppb stages. But that heat needs to get to the centers of all the boards.

From contributor B:
The wood's internal temperature needs to get that hot, meaning you need to have the kiln up a bit to get there. The time it takes depends on the thickness of the wood and the way you direct the airflow through the stack. Most people are content with 24 hours, but since you are having trouble you may choose to keep it on a little longer. A good quality laser type temperature gauge may be a good investment.

From contributor K:
I had a load of maple over the winter that I knew had bugs in it. I tried to heat my kiln to 140 and keep it there for 24 hours. I didn't run my fans during the heat and I am not 100 percent sure if the bottom layers got all the bugs killed. The bugs seem to have been killed but I want to be 110 percent sure. I have moved the wood and kept it on stickers to see if I see any sawdust. It's been 6 months now and no visible sawdust falling. Would you be comfortable using it yet? How long would you wait to see if any sawdust droppings show up ?

From contributor B:
The worry are the larvae; they can hang around in limbo for years, only to come out and mess your project up after you have finished it. There are plenty of variables here, and you may well be okay. I would bump it back into the kiln with another load (during the heat treatment only) if possible before using it if you plan on selling or giving the project piece to someone else.

From contributor R:
Contributor B is right. It happened to me after a year and a half. The lumber was ash and it had a phyto cert. It cost me thousands of dollars repairing a whole hotel. I was the buyer, so I don't know if it was kiln dried the proper way (even though it had the phyto cert).

From Professor Gene Wengert, forum technical advisor:
It is rare, but it does happen that the powderpost beetle (lyctid) can survive in dry wood for up to two years (but usually it is shorter; usually they will exit when the temperature warms up as they think it is summertime and time to reproduce) before they come out and leave the wood. During that time, they may have been boring small tunnels within the wood, weakening the wood. Of course, the heat treatment discussed will eliminate the insect, larva and eggs… at the moment.

Once treated, the wood can be reinfected, especially if the wood is in close proximity to foreign species, or an infected native wood. The heat treatment only sanitizes the wood for that moment; re-infestation is possible indeed. So, a phyto certificate is almost useless for the PPB.

Once there is a coating or finish on the wood, the insects cannot lay their eggs on a smooth surface.

Note that if the kiln is at 140 F, the wood is most likely not at 133 F throughout. Most of the time we need to have the kiln at 160 F or so. Contributor K, you may be okay, but another heat treatment at a hotter temperature is probably best.

It is really rare to have the lyctid PPB in kiln dried maple, as the wood is so smooth that the insect cannot find a place to lay its eggs (a nook or cranny). There are other insects that can get into wetter wood. Note that the lyctid PPB holes are 1/32" to 1/16" in diameter. Contributor K, did you see very small holes initially?

Contributor R, hopefully you had a good technical advisor and maybe a lawyer that could indicate that the wood was defective when you got it and that it was not recognizable by you, so you are not the one to pay the damages, but your supplier is. In fact, if the wood was infected, you should have seen evidence when you machined it. I would look for poor storage.

From contributor K:
Yes, the holes were in the wood from the start, but the log stayed on the ground a while. The holes are small and look like it was stabbed with an icepick. I can heat it again. With the heat I am using I struggle in the middle of winter to keep it as hot as needed to kill bugs, but should not have a problem now.

From Professor Gene Wengert, forum technical advisor:
If the insects came into the log, it is much more likely that they are the anobiid beetle, which does not like dry wood at all, but is a wetter wood insect. Did you notice that some of the holes had a slight dark ring at the edge of the hole? If so, that is the ambrosia beetle.