While it is true that Permethrin still works it is getting harder to get hold of in the EU and like with many chemicals (Ivermectin for example) over use will eventually lead to mites developing a resistance.We are rebuilding and fighting a retched infestation of mites. They hide at the end of the roost bars (in under and at the ends where it attaches to the wall).
I would love tips, photos or links of your roost bars that inhibit these rotten bloodsuckers. We need a new plan. I am Painting and sanding all wood today.
I use this.
No, I'm not mad. Many other experienced chicken keepers use a blow torch as well.
Yes, it takes a bit of practice but if you make your roost bars so they sit in a socket and are removable then you can remove the roost bars and apply the blue tip of the flame which is around 400 degrees centigrade to the ends of the bars and once you have gained some confidence with the blow torch to the roost bar sockets.
Nothing withstands 400 degrees centigrade. It not only kills the mites, but also their eggs which chemical sprays don't usually.
While you are rebuilding (?) consider designing your coop so that the roost bar ends are located outside the coop itself. Red mite do not like sunlight. Or, build you coop so that everything inside is removable.
The plastic rectangles you can see in the first picture below are covers for the roost bar ends. If necessary the entire roost bar can be withdrawn through the coop.
This picture shows a removable nest box and roost bare unit.
To learn a bit more about using a blow torch for eliminating pests and parasites a good place to start is with net pages on bee keeping. Bee keepers have been using blow torches to clean hives for many years.