Some beekeepers did not treat for mites and wanted to. The warm weather over the next week can make it still happen. Most colonies should have very little to no brood in the hive right now. Late fall mite treatments can be very effective. With the absence of brood in the colony all the mites are on the bees making them a good target for this type of miticide. Using Hopguard with contact strips right in the cluster of bees should provide a good treatment with only a single application.
Hopguard is safe to use and comes from the hops plant. It is considered a food additive.