I've treated all 3 chickens with poultry dust, but poor Chocolate (CM) keeps getting mites. She's getting a lot of feathers in - I can see them. But the base of the feathers also has a lot of dirt and the sheaths don't seem to be coming off easily. I gave her a bath last month and a lot of dead skin came off too. The other 2 chickens are fine. No sign of mites, feathering in nicely, etc. They are all between 18 & 24 weeks old. I dust the coop with permethrin (sp?) and use it in their dust bath (they also free range when I'm home). I use DE in with their bedding (along w/poultry dust). I just don't know why only 1 keeps showing the mites. Anybody else have a clue? And what more should I do? Thanks.