SEVIN DUST: I agree with Cindy in PA, I can't stand Sevin Dust. It is poison, and I certainly would not use it if I did not have a mite problem. That being said, most fowl mites are resistant to Sevin dust anyway and so it is not very effective. I used it in the past when I didn't know as much about it. As Cindy indicated, Sevin dust has been linked to declining bird populations, and it is lethal to honeybees & other beneficial insects. If it has some effective on "wild birds," then might it have have some ill effect on chickens. I had a hen to die of cancer (per State lab analysis) and she was one I used Sevin dust on before I knew better.
DE is no more effective as ash from your grill (good for the dust hole as well), quartz sand or any good dirt. If chickens are able to take dust baths & you limit their exposure to wild birds as much as possible & you are careful about additions to your flock, these measures is the best control against mites. DE is hype, and I really hate to see people waste their money on it. I was using DE everywhere and during its use (couple of years religiously), is the only time my chickens ever got mites. I also tried dusting down the birds solely with DE, and it did not kill the mites. I do not see any benefit to using DE.
I have used the non-toxic "Poultry Protector" for about a year now and while I am not vouching for it, I have NOT had any mites, lice nor scaly leg mite since using it.