Wood Boring Grubs - In my dried slab!

[Everest123]

I'm finishing a slab of walnut for a friend of mine and have come across two wood borers in the slab.  I cut this tree, sawed it, and it spent 3.5 months in my solar kiln over summer.  Temps peaked at 140 (probably lower where this huge slab was located).  It's around 8% moisture content.

I recently planed the slab and did some finishing cuts.  As always there are plenty of bore holes in the sapwood and under the bark.  However after finishing my 80 grit sand on the bottom of this slab, I came back a few hours later and immediately notice this: 



 

To me, that screamed (pooop!!) so I sanded the area and it immediately came off.  I then grabbed some dental picks and started fishing.  Sure enough, I caught two out of two different holes.  Here are the little buggers.



 

And here is a closeup:



 

My research suggests that there are only present under the bark (or very close in the sapwood) and my observations bear that out.  But that said.  

QUESTION: Should I be concerned about these?  My thinner boards have never exhibited this, I suspect since this one is 3" and was at the bottom of my pile, it never got hot enough to sterilize.  But I hate to give this to anyone if it's going to be an issue.  

Side note: I've build many tables and whatnot from this wood and have never had a problem.  Help!

-Jeff

[Old Greenhorn]

Wow, sorry man. That stinks. The only thing that comes to mind is hitting it with solubor asap. Won't kill them until they start eating their way out, but it is something.

[Stephen1]

I do not know what kind they are,so I'll just hang out and find out.

[YellowHammer]

Yellowhammerism "Bugs is bugs, and bugs in wood is bad."

Yes, you should be concerned about them if you are selling the slabs or giving them to a friend.  No matter what kind of bug they are, the customer or friend will not be happy, not happy at all.

You may get a reputation for bug infested wood that eventually caused termites in their house and lead to a costly divorce or the world to end.  Customers over react to hug wood.  Seen it, been there.  

These big guys are pretty juicy and would have easily been killed at moderate sterilization temperatures, and even lower moisture content.

This is why a kiln is so important.

By the way, the quality of the wood is immaculate, you did a good job with it.  

But, "Bugs is Bugs" and people don't want to buy bug wood.  

[Everest123]

Well I'm not selling this particular slab, but I have sold a few. All of them, including this one have been through my kiln and are 6-8% moisture.  But I definitely agree with you. My research suggests these are Buprestidae larvae, which don't have any tendency re-infest...but....yuck. 

I didn't think theses could survive in dry wood :(

[GeneWengert-WoodDoc]

Insects can survive for a while in drier wood, but maybe the core is wetter than 8% MC.  With dry wood, their jaws usually cannot eat successfully as the wood is so strong.  Walnut is not that strong.  Plus they do need water.

The holes in the first picture are at an angle, so they are preexisting.

Insects usually like the sapwood, as there is more sugar and starches plus no deleterious chemicals.

The general guess with dry wood at 8% MC,  and 1/16" diameter holes that you have lyctid powderpost beetles.  If the larva mature into insects with wings, they can breed and infect other pieces.

[YellowHammer]

Well I'm not selling this particular slab, but I have sold a few. All of them, including this one have been through my kiln and are 6-8% moisture.

I didn't think theses could survive in dry wood :(

Kiln Drying Yellowhammerism #2 (this topic is using a couple of them)

"Kiln drying won't necessarily kill bugs, it only makes them thirsty"


I've seen it many times.  A low temperature dehumidification kiln cycle, or a solar kiln cycle, won't kill bugs, mold, snakes, mice or much anything else.  For the big black carpenter ants, it just seems to make them angry.

Only one thing kills bugs, all the time, every time, and that's pure heat.  I do 150°F for 24 hours.  Why?  I've seen things start crawling again at 120° and even 130°.  I've never seen anything crawl after sustained 145° and that's why I go to 150°F.  That is why the sterilization cycle is so important.  It kills everything.  Nothing comes out alive. Period.  

Here is a good example of a larvae that survived a kiln drying cycle at 120°F.  It was not until the sterilization cycle that the heat became so unbearable that it had to crawl out of the wood like a Polaris Missile.  However, once it hit the hot air, it flashed off into an empty cheese puff shell before it could even exit the wood.  No more bug, nothing left but a burned out hollow crispy critter caught escaping.  It didn't even have time to scream, it just went "Poof".  Did I mention that I hate bugs in wood.  



    

[Everest123]

@YellowHammer / @GeneWengert-WoodDoc anything I can do with this slab?  I have some boracare.  Is it possible to coat it and let it dry?  I surely hate to burn this slab.

[nativewolf]

Hello Sperryville neighbor, looks like you've got the hang of sawing and drying too.  Walnut slabs can be tough to dry so congrats.  Sorry to see that grub.  The solar kiln is working out?  Maybe edge off the sap wood and look for cavities.  

[Everest123]

The general guess with dry wood at 8% MC,  and 1/16" diameter holes that you have lyctid powderpost beetles.

@GeneWengert-WoodDoc, they are more chambers than holes, and larger than 1/16th.  I've dealt with PPBs before and I think these are too large. I'll measure and will post a more exact number. But the chambers are rather large.
I'm planning to mix up a batch of boracare today and treat this slab and a few others I have. My research suggests that it will be effective since the wood isn't painted in any way, but of course I'd appreciate your input and experience as always. Thanks!
-Jeff

[Everest123]

Hello Sperryville neighbor, looks like you've got the hang of sawing and drying too.  Walnut slabs can be tough to dry so congrats.  Sorry to see that grub.  The solar kiln is working out?  Maybe edge off the sap wood and look for cavities.  

Hi there! The solar kiln works great. I've found that it actually does a good job killing insects but this is my first 3" piece. It was on the bottom of the pile and clearly it didn't get hot enough as Yellowhammer has said.  This is an incredibly beautiful piece - I'm determined to save it.

[Don P]

Since you can see all the entrance holes and it is one piece you can inject borate into the holes. It looks like you've already surfaced so I'd be leery of rewetting the entire piece. It does look to be one of the flatheaded beetle larvae, I have had them last far longer than I would have imagined in air dried, they must have been spitting cotton  :D. It does look like you need to build a hot box for behind the solar kiln.

[YellowHammer]

I would not burn that piece, at all.  

The problem is that for every hole you see on the surface, there are more that are not visible.  Spraying or surface treatments won't kill them until they go through the surface barrier.

There are only two surefire way to remove the bugs in the sapwood.  
1.  Trim off the sapwood.
2.  Get it hot and cook them.

This isn't as hard as it seems as 150F isn't that hot, in reality.  If you were to build a small wooden and foam box and put a halogen light or two in it, with a fan to circulate the air, then it would heat up pretty fast.  Don't build it in the garage in case it heats up too much, those halogen lights put out a lot of heat.  

[Everest123]

This slab is 130x25x3 - it would take a big insulated box to heat this sucker to 150. I'm pretty positive theses are flathead beetles, and they definitely are too big for PPBs

 

@YellowHammer I've thought about your earlier comment on thirst and I'm positive you nailed it.  I drive this slab to my home from my lumber shed (which I dehumidifier to 45%) and it was raining.  I covered the slab very well but the underside exactly where I found those two grubs close to the surface was exposed and got quite wet.  My conclusion - they sensed the water and moved to the surface to drink.  Here a photo of the two bore holes, with the sanding pack indicating the wet strip (the wetness covered both holes).  It was wet enough to implicate both of those bire holes.



 

I can't build a box this big at this time, so my plan is to treat with boracare and know that any nasties emerging will be killed and not pose a threat.  And I have a bunch of freshly sawn walnut and maple I need to treat anyway, so I might as well.

As always you guys are a fountain of knowledge and wisdom. Best forum on the web, by far.  :new_year:

-Jeff

[jb616]

Well I'm not selling this particular slab, but I have sold a few. All of them, including this one have been through my kiln and are 6-8% moisture.

I didn't think theses could survive in dry wood :(

Kiln Drying Yellowhammerism #2 (this topic is using a couple of them)

"Kiln drying won't necessarily kill bugs, it only makes them thirsty"


I've seen it many times.  A low temperature dehumidification kiln cycle, or a solar kiln cycle, won't kill bugs, mold, snakes, mice or much anything else.  For the big black carpenter ants, it just seems to make them angry.

Only one thing kills bugs, all the time, every time, and that's pure heat.  I do 150°F for 24 hours.  Why?  I've seen things start crawling again at 120° and even 130°.  I've never seen anything crawl after sustained 145° and that's why I go to 150°F.  That is why the sterilization cycle is so important.  It kills everything.  Nothing comes out alive. Period.  

Here is a good example of a larvae that survived a kiln drying cycle at 120°F.  It was not until the sterilization cycle that the heat became so unbearable that it had to crawl out of the wood like a Polaris Missile.  However, once it hit the hot air, it flashed off into an empty cheese puff shell before it could even exit the wood.  No more bug, nothing left but a burned out hollow crispy critter caught escaping.  It didn't even have time to scream, it just went "Poof".  Did I mention that I hate bugs in wood.  



    I haven't gotten into kiln drying yet but I was wondering about an efficient way to heat the kiln to the 150 degrees for 24 hours.  When I build my house I will have a wood boiler installed outside as well. Would this be a way to be able to heat the kiln for the 24 hour period?  What are the other methods?  thanks!

[YellowHammer]

Any kind of heat source can be used.  I use electricity in both my kilns, one with electric heat strips and another with a combination of heat strips and halogen lights. 

I have a solar kiln as well, but experience has shown that mine will definitely not stay hot enough, long enough to kill bugs.  So every load that comes out goes into one of my other kilns for sterilization.  

The heat of the sterilization cycle not only kills hugs but is very useful in the drying process.  If done slowly, over a number of days, it helps to "wilt" the wood, for lack of a better term, kind of like cooking low and slow in a crock pot.  It helps to flatten the wood under weight and also removes a lot of the internal stresses (but not all) to make it more manageable.  

[Everest123]

@YellowHammer - I've considered putting 1200 watts of heating inside my kiln.  It would sure get hot enough if I did that.  It regularly hits 130-140 in the summer, probably higher with a dry / mostly dry load inside.  It's big, but well insulated.

[Everest123]

Boracare is on board!  Thoroughly coated every surface. The crotch with bark was tricky - and thirsty.  But I got it all.  That part took the most liquid by far.  I'm feeling pretty confident that'll take care of any future problems.

 

 

[Everest123]

Corrected photos...oops.



 

 

[Mike W]

The heat of the sterilization cycle not only kills hugs

............ Hmmmmm, where to go with this??? 

[YellowHammer]

Now that's a Yellowhammerism!  Autocorrect at its best!  

Also, that's a beautiful slab of walnut.  Let the thirsty little beggars drink some of that!

[Brad_bb]

My thinner boards have never exhibited this, I suspect since this one is 3" and was at the bottom of my pile, it never got hot enough to sterilize.

Exactly.  The thicker it is, the longer it will take the heat to penetrate and probably more temperature will be needed.  Of course the sterilization comes after drying.  They will not go into dry wood.  I see these grubs alot under the bark.  Reminds me of a cobra.  Not sure what kind of beetle they are.  Maybe someone will tell us?  The only thing that goes into dry hardwood that I know of is Powder Post Beetle larvae.  

Just fill the holes with some fast curing epoxy like West Systems or similar if they bother you.

[terrifictimbersllc]

"Kiln drying won't necessarily kill bugs, it only makes them thirsty"

There you go, that's a good one

Wife and I watching a Pawn Stars episode other night where Chumlee was following the Old Man around writing down his sayings ("Aphorisms"). 

[Everest123]

My thinner boards have never exhibited this, I suspect since this one is 3" and was at the bottom of my pile, it never got hot enough to sterilize.

Exactly.  The thicker it is, the longer it will take the heat to penetrate and probably more temperature will be needed.  Of course the sterilization comes after drying.  They will not go into dry wood.  I see these grubs alot under the bark.  Reminds me of a cobra.  Not sure what kind of beetle they are.  Maybe someone will tell us?  The only thing that goes into dry hardwood that I know of is Powder Post Beetle larvae.  

Just fill the holes with some fast curing epoxy like West Systems or similar if they bother you.

I'm nearly 100% sure they are some species of Flathead boring beetle.  there are many species and I wouldn't know which based on the larva but if you Google and look at the images that's exactly what came out of this lab. The behavior is also the same as described for that type with most of the tunneling those directly under the bark.  The larger tunnels (two in this slab) go into the sapwood and that's where I found those grubs.  
They are all dead now I can tell you that or they will die when they try and emerge. I saturated this slab in boracare.   Too much in fact. I had to wash it off and dry it for two days to get a clean sanding surface.  
Die!!!!
Thanks for the kind words @YellowHammer .  I will post a photo when I finish this slab. It's quite spectacular. 
-Jeff