Several of my birds have this white matter on their vent-area feathers. I'm not able at this time to have a closer look (eye surgery), so I treated with ivomectrin drops and sprayed permethrin liberally in the coop after a good cleaning. New bedding, etc. They got spooked when I was doing the drops so, with all the flapping, I may have not gotten all the drops onto the skin but I'll redo in 10 days and should be able to do a better job of it then. It's been very wet and humid all summer, so the dust bathing has been sporadic. What ingredients should I put into a dust bath mix that would help in my pest-control effort? I'm thinking sand, some permetrin dust powder, a bit of peat moss? I have no wood ash and won't be able to burn anything right away.