How Much Oxalic Acid Per Hive? Dosage, Timing and Schedule for Vaporization

How Much Oxalic Acid Per Hive? Dosage, Timing and Schedule for Vaporization

"How much oxalic acid do I put in?" is the question we get more than any other, on the phone, by email and at every bee club we visit. The short answer is easy. The useful answer is that the dose matters less than the timing, and once you understand why, the whole year's treatment plan falls into place.

Here is what the label allows, what we recommend, and the schedule that thousands of InstantVap customers have used for years.

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The Legal Dose Just Went Up

For years the EPA label on Api-Bioxal limited vaporization to 1 gram per brood box. That label has now been updated to allow up to 4 grams per brood box. If you have old oxalic acid on the shelf, the package may still show the older number; the current label is what governs, and only EPA-registered oxalic acid such as EZ-OX is legal to use in a hive. Hardware-store wood bleach is not, no matter how pure the bag says it is.

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What We Actually Recommend: 2 Grams Per Brood Box

Most of our customers have had success for years with 2 grams per brood box, not exceeding 4 grams per hive. A single deep gets 2 grams. A double deep gets 4 grams. That is the dose we use in our own yards, and it is why the InstantVap dispenser adjusts tool-free from 1 to 4 grams: dial it once for your hive configuration and every treatment is identical.

You will see recent university studies reporting that 4 grams was needed to control mites when brood was present, and that 1 or 2 grams "did not work." Read those studies closely and you will notice they applied the dose once a week for three weeks. The dose isn't the issue in those trials; the interval is. A weekly schedule leaves gaps that a summer brood nest will fill with newly emerged mites. Two grams applied on the right schedule has cleaned up more colonies for our customers than four grams applied on the wrong one.

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Why Brood Decides Everything

Oxalic acid vapor only kills mites that are out on adult bees. Mites under capped brood are untouched, and roughly two-thirds of a summer colony's mites can be under cappings at any moment. Every treatment kills the exposed mites; then more emerge with the next batch of brood. So:

• More brood = more treatments to get the same result.
• Less brood = fewer treatments.
• No brood = one treatment does the whole job.

That is the entire logic of oxalic acid vaporization. Everything below is just that rule applied to the calendar.

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The Schedule, Season by Season

Our summer treatment routine walks through the heavy-brood schedule day by day, with what to expect on the sticky board between treatments.

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The Two Best Treatment Days of the Year

If you only do two things with your vaporizer all year, do these:

1. The last 50°F day of the year. When the forecast shows daytime highs dropping below 50°F for good, the queen has shut down or nearly so, and almost every mite in the hive is riding on an adult bee. One 2-gram-per-box treatment on that day hits more mites than a week of summer treatments, and it sends the cluster into winter clean.

2. The first 50°F day of the year. When the first warm day arrives in late winter, the colony is still nearly broodless but the queen is about to ramp up. A single treatment then knocks the surviving mites down before they can move into the spring brood. Colonies that get this treatment start the season on a completely different footing; our customers tell us it is the difference between a hive that builds and a hive that limps.

You do not need to open the hive for either one. With an InstantVap, the vapor goes in through the entrance, the cluster stays warm, and the whole thing takes about a minute per hive.

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The "Once a Month" Approach

We will be honest about this one: there is no study behind it, just a lot of independent beekeepers telling us the same thing. A large share of our customers have settled on one treatment per month, all season, instead of a big catch-up cycle in August. Their reasoning is simple: mites never get a head start, the sticky board never shows a scary drop, and each treatment takes minutes. It is not a replacement for a mite wash, and it is not what the studies tested. But when dozens of people arrive at the same routine on their own and keep their bees alive, we pass it along.

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Swarms and Packages: The Cleanest Treatment You'll Ever Do

A fresh swarm or a new package is a rare gift: every mite in that colony is exposed, because there is no capped brood to hide in. You could treat on day one, but a colony that hasn't settled can abscond, and a hive full of vapor won't help. Wait until the queen is laying: once there is brood in the hive, the bees will not leave. Then, any time before that first brood is capped, give the colony a single 2-gram treatment. That one dose can clean the colony almost completely and give it a mite-free start on its first brood cycle. We have step-by-step guides on treating a swarm and treating package bees.

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Don't Guess: Wash Before and After

Every schedule above assumes you checked. Do a mite wash on a representative colony before you start (we use the Easy-Check), and again two to three weeks after your last treatment. Above 3 mites per 100 bees in summer or 1 per 100 in winter, treat. Below that, put the vaporizer back on the shelf and check again in a few weeks.

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Want the full comparison of oxalic acid against Apivar, Formic Pro and the rest, with the study numbers? Read our Varroa Mite Treatment Guide.

Happy Beekeeping from the Lorob Bees Team

Keep reading: Explore all Lorob Bees beekeeping guides — varroa, oxalic acid vaporization, pests and diseases, all in one place.

Dosage and schedule recommendations above reflect Lorob Bees' field experience and customer feedback. Always read and follow the label of the specific EPA-registered oxalic acid product you use.