Ditto using the dust. Make sure you cover your mouth and nose when you apply it. Also, replace the bedding/straw in your coop and work the dust into the roosting bars and nooks and crannies and cracks of the coop.
When I "dusted" my chickens, I did so at night. I removed them one at a time from the roosting bars and put then in plastic tub and then worked the powder into them around the vent, breast and under the wings. Try to avoid getting it in their eyes and mouths. This little gizmo helped me apply the dust:
Mites and lice tend to take hold in the winter, because the chickens often no longer have an area to dust bath in. If (or when) you have the space for it, set up a dust bath station -- loose dirt, sand and/or wood ash -- somewhere out of the elements.
