Oxalic Acid Vaporization Dose: How Much Per Hive?

The OA vaporization dose is simple: 1 gram of oxalic acid dihydrate per hive.

This doesn't change based on the number of boxes on the hive, the size of the colony, or the time of year. It's a flat 1-gram dose per hive unit.

TL;DR

Oxalic acid (Api-Bioxal) is approved for dribble and vaporization methods; both kill only phoretic mites on adult bees
Vaporization is more effective than dribble when brood is present because bees can contact vaporized acid across the colony
The extended vaporization protocol (every 5 days for 3 applications) compensates for mites in capped brood
Oxalic acid has no PHI restriction for honey supers when used according to the Api-Bioxal label
Efficacy during true broodless periods can reach 95%; with brood present, efficacy drops to 50-70%
Always wear a respirator and eye protection during vaporization; oxalic acid vapor causes lung damage

Why the Dose Stays Constant

Oxalic acid vapor distributes through the hive via air circulation and bee movement. The 1-gram dose was calibrated to produce an effective vapor concentration throughout a standard hive volume. Additional acid doesn't improve efficacy, it increases risk to bees without benefit.

Whether you have a single 8-frame medium, a double-deep Langstroth, or three boxes stacked, the dose is 1 gram.

Multiple Hives in a Single Session

If you're treating multiple hives:

| Hives to Treat | Total OA Needed |

|---------------|----------------|

| 5 hives | 5 grams |

| 10 hives | 10 grams |

| 25 hives | 25 grams |

| 50 hives | 50 grams |

Measure each dose individually into the vaporizer cup before each hive. Don't try to pre-mix or eyeball, precise dosing matters for both efficacy and safety.

Treatment Schedule by Season

Broodless period: 1-2 treatments, 7 days apart

Active brood season (extended protocol): 3-5 treatments, 5-7 days apart

|---------|-----------|---------|------------------|

| Broodless (1 treatment) | 1 |, | 1g |

| Broodless (2 treatments) | 2 | 7 days | 2g |

| Extended brood-present | 3 | 5-7 days | 3g |

| Extended brood-present | 5 | 5-7 days | 5g |

Equipment Needed

For 1-10 hives: Any commercial OA vaporizer (entry-level units $50-100 work fine)

For 10-50 hives: Battery-powered vaporizer or torch-fired commercial unit speeds the process

For 50+ hives: Powered units with continuous operation capacity

Always required: P100 respirator, safety goggles, nitrile gloves

Safety Reminders

Load and operate the vaporizer away from your face
Seal the entrance before activating; wait 10 minutes after sublimation
Work upwind of the hive
Let the vaporizer cool before transporting to the next hive
Keep children and pets away from treatment area

FAQ

How many grams of OA per hive?

1 gram of oxalic acid dihydrate (Api-Bioxal) per hive, per treatment. This dose applies regardless of hive configuration, single, double, or triple boxes.

Can I use more OA for a stronger effect?

No. More OA does not increase efficacy. The 1-gram dose creates effective vapor concentration in a standard hive. Overdosing can harm bees and doesn't improve mite kill. Follow the label.

What OA product should I use?

Use only FDA-approved Api-Bioxal for honey bee treatment in the US. Don't use food-grade oxalic acid purchased from other sources, it's not labeled for bee treatment, the concentration may differ, and using it would be an off-label application.

How many oxalic acid vaporizations can I do per year?

The Api-Bioxal label allows up to three vaporization treatments per year per hive. Under the extended protocol for colonies with brood present, three applications spaced 5 days apart count as one treatment event. Always follow current label instructions as registration requirements can be updated.

Can I use oxalic acid from the grocery store instead of Api-Bioxal?

No. In the United States, only EPA-registered Api-Bioxal is legal for treating honey bees. Industrial or food-grade oxalic acid is not registered for bee use and cannot be used legally. Using unregistered products violates federal pesticide law and may affect honey marketability. Api-Bioxal is widely available from beekeeping suppliers.

Is oxalic acid safe to use on brood?

Oxalic acid in dribble form is damaging to brood when applied directly; the label specifies use on broodless colonies for dribble application. Vaporized oxalic acid is less directly damaging to brood than dribble and is approved for use with brood present, though efficacy on mites in capped brood is limited. Always follow the label for the application method you are using.

Sources

American Beekeeping Federation (ABF)
USDA ARS Bee Research Laboratory
Honey Bee Health Coalition
Penn State Extension Apiculture Program
Project Apis m.

Track Each Treatment Session

Log your treatment date, hive count, and dose used in VarroaVault. Schedule your post-treatment count reminders and verify efficacy after each OA session. See the full winter treatment protocol.

Get Started with VarroaVault

Oxalic acid is one of the most effective and accessible varroa treatments available, but timing and application method determine whether you get 95% efficacy or 50%. VarroaVault tracks your broodless window, application method, and pre/post mite counts so you can see what's actually working in your operation. Start your free trial at varroavault.com.