Second Formic Acid Treatment
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The second treatment does not follow a fixed calendar interval but the feeding schedule: it follows once the winter feed is in the colony, usually in early to mid-September.
The second treatment does not follow a fixed calendar interval but the feeding schedule: it follows once the winter feed is in the colony, usually in early to mid-September. It catches the mites that were still in the brood during the first round and have since emerged.
This is actually the decisive treatment of the year: the winter bees are now developing, and only a colony with undamaged winter bees makes it through February. Anyone who postpones it often loses the colony only in late winter, seemingly for no reason.
Again: count before and after. If the infestation stays too high, another round is needed. Final certainty comes from the winter treatment during the broodless period.