VTBeeHannah · Vermont, US · Pests & Disease · Sep 12, 2026

Does oxalic acid do anything in September with brood present? Planning for the broodless window instead

Vermont, second year, three hives. Formic Pro came off late August and my verification wash this week says 4, 3 and 5 per 300, so lower but not the under-3 I wanted. A club member's advice was "just vape them with oxalic now, then again in two weeks, then again". I don't want to do that without understanding it, and I've read that oxalic barely works with brood in the hive. Can someone explain WHY it doesn't work well in September? Is it that the mites are hiding under cappings, or something else? And if the right plan is to wait for the broodless period, how do I actually know when my colonies are broodless here — is it a date, a temperature, or do I have to open them up in December to check? I'd rather do one treatment right than three treatments wrong.

#oxalic-acid#varroa#broodless#fall-treatment

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1 reply

ImkerinLena · Sep 12, 2026 · ✅ Accepted answer

You've reasoned it out already. Oxalic acid only kills mites on the bees and does nothing to mites under cappings — and in September most of them are inside cells with the last brood. One application hits a minority, and the label allows one application per broodless period, not a series with brood in. Your numbers aren't an emergency. Recheck in three weeks and plan the oxalic for the broodless window: in Vermont that's typically late November into December, after a few weeks of hard frost. Verify by pulling a centre frame on a mild day — no capped brood, treat that day. Label rate, once.

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