There is some truth in many of these home brew solutions to parasites and chicken health in general. The general rule as with most things is keep an open mind but not so open that your brain falls out.
Wood ash comprises very fine particles. In theory if you cover a mite in very fine dust it will suffocate. Throwing a light coating on top of some feathers hoping that a mite is stupid enough to roll around in it seems a rather forlorn hope imo. If you've ever dealt with mites you will know that as soon as you part a chickens feathers to look for them they scury off to somewhere with better cover, on the chicken of course. Even lice, which to me at least don't seem as mobile, or as intelligent as mites, will try and hide as soon as anything invasive disturbs the chicken feathers. Finding mites is like hunting in a way. You have to sneak up on them and chase the little feckers. During the chase one is likely to find that there are quite a few more, all trying to hide.
Lots of chickens ime carry a few mites. When you can see lots easily, you, but more so the chicken, has a problem. You could sit there for countless hours chucking handfulls of wood ash at them and you might get one or two. Essentially this is what chickens do in a dust bath. They scratch up a a bit of dust and chuck it over their backs. The front part of a chicken of course is in the dust and this will work a lot better than the chucking dust approach. One will have noticed that despite a chickens best contortion acts when dust bathing they don't seem to do that unpside down stuff so their backs and under their wings etc doesn't get much of the dust at skin level. The mites seem to know this. In fact, come chicken bath time if you listen carefully you can hear the mites shouting to each other "bath time chaps. Everybody head for high ground."
It would be wonderfull if we could all go the right on organic route and give the chickens something harmless to both them and the poor little mites that would just make the drop off and go elsewhere. I don't believe in Santa Claus either.
The horrible truth is, if one of your chickens has gots mites and you've noticed then there are lots and lots of them. As mentioned, you can plot up in the feathers and take pot shots at one or two as they pass or you can just nuke the lot and be done with the problem.
Current easily delivered nuke option is a chemical called Permethrin. Mites don't like it.
What gets overlooked more often than I would like is it doesn't matter what you use, it's a chemical of some sort most of the time; sulpher, lime deet, whatever. Some chemicals some people have designated as "bad"chemicals and others as good chemicals.
I like those get the job done chemicals.
Sod em.
. Think that I shall do both : 
