IMO, don't treat unless you see bugs.@aart, we're going to check the birds tonight to see if they need treated at all. I got the Permetherin because we've had chickens for about 8 years and have never treated them with anything but DE. They don't seem to scratch much but we thought we'd better check and then be ready to treat them if they need it. Um .... what should we look for?
Bugs check Blurb
Have you checked them over real well for mites and/or lice?
Google images of lice/mites and their eggs before the inspection so you'll know what you're looking for.
Part the feathers right down to the skin around vent, head/neck and under wings.
Best done well after dark with a strong flashlight/headlight, easier to 'catch' bird and also to check for the mites that live in structure and only come out at night to feed off roosting birds.
Wipe a white paper towel along the underside of roost to look for red smears(smashed well fed mites).