How do you prevent northern fowl mite?

Wash down your whole chicken house with lime and water paste. When dry, sprinkle food grade diatomaceous earth all over the coop, nesting boxes and dust bath area, and dust every few weeks thereafter. Paint old motor oil onto roosts using a brush especially getting into the cracks on the underside. Add a crushed clove of garlic to the waterer and replace every few days. This method beat the mites that had wiped out my whole chicken house, and now my chickens are happy, healthy and mite free.