Copied from old posts:
https://www.backyardchickens.com/forum/viewtopic.php?id=226143
https://www.backyardchickens.com/forum/viewtopic.php?pid=2525157#p2525157
The definite no-questions way to treat lice and mites is use permethrin dust on the birds or ivermectin in the older birds (see below about using wazine first), and use permethin liquid (goat lice spray - read the label) on the wood, 3' up from the bedding, and in the eyes and cracks and joints of the wood near nest boxes, on roosts, etc.You can worm the next day and get it all done. Give them all yogurt that day. (Put them out of the coop when you're spraying the wood). The permethrin doesn't penetrate them.
Then in 2-4 weeks, you can use ivermectin (5% cattle pour-on, the blue liquid - I buy generic ivermectin) on your adult birds birds to kill blood-taking parasites. You will want to repeat the wazine treatment for the babies at that time. Wazine is meant to be repeated as it only kills adults. In birds not wormed over six months, I would always recommend wazine first anyway as you don't know the parasite load. Too many parasites (larva and adults) dying at once with ivermectin might be too stressful on them, particulary if they've been battling mites.
You can use ivermectin on them at 4 months old. Use the 5% cattle ivermectin pour-on, the blue liquid. On the ivermectin pour on, I use 1 drop for a small OE hen sized bantam, 2 drops for an OE male to a regular small bantam, 3 drops for an average bantam or very small commercial hen, 4 drops for an average adult chicken or small large-breed hen, 5 drops for a large large-fowl bird, and 6 drops for giant breeds, a large bird. That's the blue "ivermectin" not any other '-ectin'.
I use a 3 cc syringe with a 25g needle. I of course don't inject, but I find the needle makes a very precise size of drop and allows me to place it better. I hold the syringe horizontally in case the chicken hops up so I don't poke it. Then you just have to find a very naked spot on their skin - between their shoulders or at the back of their neck works best for me. If you get it on any fluff, it will absorb into the fluff at lightening speed and then you don't know if they get it or not. So aim for very bald skin on their main body.
I treat withdrawals just as indicated for cattle. Ivermectin is not at all labeled for chickens, so we don't really know. However since it is used to treat worm infestations in humans - I like to assume that the amounts in eggs are probably safe for humans if not pregnant. However, I don't like the thought of worms being shed into an egg - so I personally withdraw for 2 weeks "just because it's icky" - such a scientific reason.
Levamisole is also a good choice if you choose it. I simply like ivermectin because it's quick, easy, safe, gets externals.
Unfortunately, mites are too dangerous to go with organic methods which will not kill them. I would recommend you use it if it worked. The permethrin dust is a chemical version of a dust that was once made out of flower petals. It's very safe, much different than things like sevin dust. Mites will take birds down very very quickly.
And if you use permethrin, dust them thoroughly. Yes the younger birds can withstand it.
So my suggested game plan:
Day one: Treat the bedding and birds with permethrin dust. Spray the coops with the permethrin liquid, goat lice spray or with the dust made into a "paint" with water. Paint the legs of the birds again with olive oil , possibly with a little tea tree oil in it, just a tiny bit. (Say you make 1/2 cup of oil, use 3 drops of pure tea tree oil). You'll get the leg mites on the 2nd worming.
Day two: Worm with wazine in the water, all birds. Feed them some yogurt.
Seven days later: redust with permethrin to get hatching lice.
Two to four weeks from first treatment.
Worm all adults with ivermectin pour-on. That will take care of the remaining adults, the larva, and leg mites. Retreat the babies with wazine.
When babies are four months: Worm with ivermectin pour-on. Don't re-worm until your twice annual worming.
Thereafter: worm adults and birds "of age" with ivermectin - in the fall and spring is when I do it.
