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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4 replies
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.
QuebecBees · Sep 12, 2026
Quebec follows the same logic and we go broodless a little earlier than you. My tell: three weeks of nights well below freezing and a tight daytime cluster, then a five-minute look on a calm day above 5°C. I dribble rather than vaporise, mixed exactly to the label dilution, once. The colonies come out of it with the lowest counts of the year, and that's the count that matters in March.
MayaBees · Sep 13, 2026
Good on you for questioning the "vape every week" advice — it's everywhere and it's the wrong lesson from oxalic being cheap. One thing to plan for: if your recheck in three weeks creeps upward instead of holding, that's reinvasion from a collapsing colony nearby and you'd want to deal with that before winter, not just wait for December.
VTBeeHannah · Sep 13, 2026
That all makes sense — mites under cappings, one shot in the broodless window, verify by looking not by calendar. Recheck on the calendar for early October and Api-Bioxal on the shopping list. Thanks ImkerinLena and QuebecBees, and MayaBees I'll watch the trend.