Woodworm in garage

[2stis]

I'm currently converting a barn into a better space for use as a garage. The joists on the lower floor were exposed and there was lots of muck, cobwebs, etc. up there that was falling onto the cars so I am boarding over it to create a ceiling for the lower floor. In some areas I noticed that woodworm have taken up residence (lots of flight holes visible) so I am treating the area with a Permethrin-based woodworm killer that I am brushing on.

What I really want to know is how effective is this at killing the woodworm and keeping them away in future - can I sleep easy that they will all be killed as a result (how far will the Permethrin penetrate into the wood?) or do I need to keep removing the ceiling over the next few months and years to check that they are not still attacking the wood below? The joists themselves (8 by 2s I think) are still very solid and don't show too much sign of flight holes, so should be fine as long as they don't get attacked more, but a number of the thinner boards forming the floor for the upper level are riddled with flight holes so I think I'll be replacing a number of those even thought they have now been treated.

[crankedup]

My understanding is that once treated that should see and end to the woodworm, as they chomp their way out of the wood ready to make flight and breed the chemical will sterilize them, hence no woodworm next time around. I believe this is how the chemical concerned works or I could be mistaken it for an alternative, either way once treated you should be OK. Alternatively you could use a chemical paste which is daubed onto the areas, this then penetrates even deeper over a period of time into the wood, I used this about twenty five years back and it worked a treat, although we have since moved house.

[Mr GrimNasty]

Permethrin is a low to moderate persisting nerve toxin/insecticide that despite being 'safe' has anecdotally made some people ill. It will not permanently treat timber but poison everything that it contacts initially, or that subsequently eats treated wood. Like most liquid treatments it probably only permeates 4-6mm with 2 or 3 applications. The effectiveness certainly wears off in the medium term.

I think stuff like Boron Ultra 12 is a more permanent treatment more specific to woodworm and 'friendlier' all round.

[2stis]

Thanks both. I read about that Boron stuff but initially thought you needed to drill out the wood and put sticks of it in, but I now read that there is a paste and a liquid too. I'll try that next time if this doesn't sort it then!

I did read some nasty things about Permethrin, as you say, so I am taking good precautions with full face mask, gloves, eye protectors and limiting myself to only doing short stints of it in any day.

Do the woodworm have to come out into the open air in order to breed once they become adults? I'm most worried that they could eat away at the beams under my new ceiling in the voids around the beams without me knowing, but if they need to eat their way out through my new plywood ceiling then at least I'll know that they are still active and can retreat. It is possible that they will be much reduced (or now gone) anyway as I think the previous owner had let the wood get wet as there were a few holes in the barn roof that I think were regularly letting water in over a number of years. Now that I have fixed the holes with some new felt it is pretty much bone dry in there, so I am hoping that alone will make a big difference to their attack!

[Mr GrimNasty]

Woodworm larvae have to emerge as beetles, fly, breed, and find suitably moist/nutritious wood to lay eggs again. Anything that disrupts that means the infestation will just die out once the generations present turn to beetles i.e. physically enclosing all the wood surfaces would stop any spread/re-infestation. Just because there are lots of holes does not mean you have a live infestation (although in an unheated garage it is more likely you do). The best way to find out is to enclose an area in polythene and check for any little brown beetles after warm weather spells throughout spring/summer.