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💧 Oxalic Acid Dosing

Label rates scaled to however many hives you're walking out to.

Read this first. Oxalic acid is a registered pesticide and the label is the law. This tool does the arithmetic off the current Api-Bioxal label rates — it does not replace the label on the package in your hand, and rates differ between products (Api-Bioxal, EZ-OX and VarroxSan are not interchangeable). Vaporizing demands a proper acid-gas respirator, not a dust mask: the fumes will scar your lungs and your corneas. Goggles and acid-resistant gloves for every method. Never vaporize into a hive you haven't sealed, and stay upwind.

Method

Hives to treat

Occupied seams per hive

A seam is a gap between two frames with bees visibly in it. Count them with the lid off before you start.

Mixing the dribble solution

Api-Bioxal	—
Sugar	—
Water	—
Makes	—

Label rate is 35 g of Api-Bioxal per 1 litre of 1:1 sugar syrup (sugar by weight, water by volume). Mix the syrup first and let it cool, then stir the acid in. Use it the day you mix it — dissolved oxalic acid breaks down into HMF over time, and old solution has killed bees.

Making OA/glycerin pads

Not a registered product. The EPA has left “own use” of oxalic acid to each State Lead Agency, so in Pennsylvania this is the Department of Agriculture's call — ask them before you make a batch, and ask about a Pesticide Research Authorization. You cannot make these for anyone else, sell them, or carry them to someone else's hives. VarroxSan is the registered, off-the-shelf version of the same idea. Safety glasses and waterproof gloves throughout, and keep a jug of baking soda water (1 cup per gallon) beside you.

Ratio	1:1 by weight — equal weights of oxalic acid dihydrate and vegetable glycerin. Weigh both; do not measure glycerin by volume.
Per hive	50 g oxalic acid + 50 g glycerin for a double-deep hive — one full Swedish sponge, cut into two pads
Heat to	Under 160 °F, stirring constantly. Crystals dissolve from about 110 °F. Past 170 °F it bubbles and breaks down.
Soak	Acid into the pan first, glycerin on top, heat and stir until completely clear, then stand the pads in the hot solution on edge and turn them once. Cold solution will not soak in.
Cure	Drain any excess, then leave the pads a day before use. White crystals on the outside are normal.
Apply	Two pads flat across the top bars between the brood chambers, one front, one back — inside the cluster where bees walk over both sides. Under the lid they do nothing.
Leave in	60–75 days, or until the bees have chewed up most of them. A pad still working feels damp and tastes sour on a fingertip; a dry pad is finished.

Cardboard version: plain chipboard cut to 1.5 × 15 inches, 3–4 hung per brood chamber between the frames, about 20 g of solution each (50 strips to a 500 g + 500 g batch). Chipboard absorbs slowly — give it hours or overnight with the pan kept warm. Source: Randy Oliver, scientificbeekeeping.com, “Extended-release oxalic acid for varroa management,” updated May 2026.

The label rates

Method	Rate	Notes
Dribble	35 g per 1 L of 1:1 syrup; 5 mL per occupied seam, 50 mL per colony maximum	Works best on a cool morning while they're in a loose cluster. Warm bees scatter and you dose them unevenly.
Vaporization	4 g per brood chamber	Seal the entrance and any cracks, vaporize, leave sealed about 10 minutes, then open up. 4 g is the June 2025 Api-Bioxal label. Packages printed with the older label still allow only 1 g per brood chamber — same powder, but the label on your package is the one you follow.
Extended release	4 VarroxSan strips in the lower brood chamber; on a double deep, up to 2 more in the top box only if it's fully populated with bees (6 max, not 8) — left 42–56 days	The one oxalic method that keeps working as mites emerge from capped brood.

Timing beats dosing. Oxalic acid cannot reach a mite under a capping — dribble and vapor only kill what's riding on adult bees. With brood in the hive that's maybe a third of your mites, which is why a single fall dribble on a brood-full colony disappoints so many people. In our part of Pennsylvania the broodless window usually falls somewhere from late November into December. Hit that window and one treatment can take out the great majority of the mite population. Otherwise use extended-release strips, or a product that penetrates cappings.

There's a second broodless window most people miss, and it's in summer. Any colony you make queenless runs itself out of capped brood — a walk-away split, or a hive that has swarmed. Once the last old brood has emerged and before the new queen's eggs are capped, there is nowhere for a mite to hide. That gap is usually about a week, it lands in the middle of summer when mites are building, and it costs you nothing to use. The split & queen timeline works out the exact dates for your hive.

Honey supers. Oxalic acid is exempt from residue tolerance requirements, and the Api-Bioxal label permits use with supers in place — one of the few treatments that does. Confirm it on your own label before you rely on that, and understand it's still not a great idea during a flow: the treatment works poorly with a full brood nest anyway.

Compare this against other treatments →