Permethrin works fine in the coop, and is approved for chickens, unlike carbaryl, which has fallen off the approved list. I would return the Sevin and get permethrin instead. It comes a 'Poultry Dust" or as a liquid, which would be easier to spray vertical surfaces. I clean out the bedding and use permethrin dust on the floor under the new bedding. DO NOT spray the yard, you will only kill every beneficial out there! You can dust each bird with permethrin, or use the Ivermectin totally off label on each bird, and repeat in ten to fourteen days, if needed. WEAR A N95 dust mask when using any dust type product, and cleaning the coop. I had to treat for mites this spring, and have been clear since. I go out with a flashlight at night and check birds, especially around their vents, where the bad bugs tend to show up. UGH! Really, it will be fine, and it's part of management when you have chickens. Mary