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I've been working with ash lately, turning several bowls and using for jaws in a workbench. A fellow woodworker was explaining some of the effects of the emerald ash borer to me and how it's affecting tens of millions of trees in North America. One strategy apparently in addition to removal is to slow the death of infested trees with pesticide.

If the situation were much less serious, I'd be tempted to joke about the abundance of new material for woodworking, but this is a real problem. I'm curious whether there are any safety concerns due to working with what is probably a lot larger volume of ash wood that has been previously treated with pesticide? Would the sawdust produced be more toxic than normal, for how long, etc.?

I already take precautions with dust (extraction, personal equipment, etc.) but should previous tree pesticide use change that equation?

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    I think you're going to need an expert's view on this to be reassured, and actually with this sort of thing the consensus view of experts not just the opinion of one. My suspicion is there's no real concern, since pesticide will be exactly like wood preservative in that you'd need to use complete immersion and high pressure to get anything more than the shallowest of penetration. Are they spraying the sawn lumber or is this just treatment of the standing trees?
    – Graphus
    Jan 30 '20 at 14:33
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    @Graphus I think the issue is that certain pesticides for this problem are not just topical. It is actually either injected or absorbed into the tree itself. There are several of course, but this is one: en.wikipedia.org/wiki/Imidacloprid#Health_impact Personally, I would probably treat it like pressure treated; I would not use it in any application in contact with food or little ones and PPE should always be used anyway.
    – UnhandledExcepSean
    Jan 30 '20 at 14:39
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    Borers are difficult to control with pesticide. They are in the trunk where pesticide does not reach. So a systemic pesticide is needed and that is a very large amount and large expense for a tree and worse for more than one tree. On a personal basis , I have found killing borers in oaks and fruit trees with a wire pushed into the hole works fine.
    – blacksmith37
    Jan 30 '20 at 21:14
  • @UnhandledExcepSean, TVM.
    – Graphus
    Jan 31 '20 at 7:41
  • @jdv, TVM. I need more characters to post this...
    – Graphus
    Jan 31 '20 at 7:41
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In the interest of building a decent article, here's what I have gleaned from a little internet sleuthing.

The idea is to get pesticides into the canopy, and under the trunk-wood, but not in the sapwood (as I suggested in a comment). This breaks the lifecycle and also gets the larva where they do the most damage.

Some of the soil, trunk-injection, and trunk-spray based treatments for Emerald Ash Borer contain pesticides like imidacloprid and clothianidin. At least one of these are common in the cocktails used for making pressure treated lumber.

This would suggest that using such lumber for indoor use might not be recommended. However, current treatment concentrates on the trunk and canopy, and even soil-based treatment should not enter the heartwood. And none of the treatments are remotely like PTL, where lumber has the chemical cocktail driven deep into the heartwood. In the case of an ash tree, once you strip off the trunkwood and any damage there made by the pest, it looks like you have reasonably safe lumber.

So, this is my weak conjecture that previously treated ash can be safely used for lumber in the usual way, at least for furniture and so on. Maybe I'd refrain from using it for bowls or other food use items simply out of an excess of safety; there might be better lumber you can use for that. And I'm probably not going to run out and carve wooden blocks and toys out of this stuff for babies.

I'm hand-waving over the recommendations for how treated ash timber and fresh sawn lumber is transported and stored, as there is evidence that such material is a vector for passing the pests on to other areas. So, follow your local laws about that. Also, take the usual care one should take when sawing any lumber up; even the cleanest organic lumber is toxic when turned into a fine, breathable dust.

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  • I appreciate this summary and I'll probably err on the side of caution with my woodworking. I've been doing a lot of work with "urban lumber" (acacia and mesquite mostly) and have thought more about avoiding the shiny objects like nails than I have pesticides, etc. Often I don't really know the origin/history of the wood I use, not that I would at a lumber yard either. For those interested, I found that Wikipedia also has a good article about the emerald ash borer and economic/environmental impact for anyone wishing a good overview.
    – gcbound
    Feb 1 '20 at 14:50

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