I just put down dolomite limestone powder in sleeping quarters of all my chu; which are all open air until I cover them for winter. There are warnings about using dolomite; I haven't read them all and have disregarded most; but made sure for adequate ventilation; it is caustic when wet, like lye, I suppose. Some people advocate dusting the birds with calcium hydroxide (hydrated lime) or sulphur; though I would be cautious about sulfur, particularly. And I wouldn't think they would do well to have to breathe any of that stuff.
If they can free range some, that seems to help; being stuck in the same place where those things breed and multiply means they are going to stay concentrated; having lots of chu in same place makes it worse. I haven't made it a point to try to eradicate them, I just keep an eye on the areas around their necks; I've got some still recovering from sickness that don't wander far, and they had them the worst prior to the dusting. It really seems to help.
