Fall mite treatment determines spring colony survival more than anything else

Varroa destructor mites are the leading cause of winter colony loss. Per the Bee Informed Partnership survey, colonies entering winter with mite loads above 3% (alcohol wash) have dramatically higher winter mortality. Treat in August-September — not October, which is too late for bees to raise healthy winter bees. Oxalic acid vaporization (when broodless) or formic acid strips (when brood is present) are the most effective treatments.