How to Treat Varroa Mites with Oxalic Acid Vaporization

Oxalic Acid Vaporization treat Varroa Mites

Beekeeping often starts with a classroom lesson or two: you pick up the basics of feeding, hive inspections, and managing common threats like wax moths or ants. But one pest quickly becomes the central focus—Varroa destructor, the varroa mite. Many beekeepers learn the hard way that varroa is a leading cause of winter losses. In fact, it’s estimated that a significant percentage of bee colonies in the United States fail each year, with varroa mites playing a major part in those losses.

Over several seasons, I’ve experimented with different approaches to control varroa. In this post, I’ll share how my beekeeping journey evolved: initial attempts at treatments, missteps along the way, and the method I now rely on—an oxalic acid vapor (OAV) schedule that has transformed my colony survival rates.

Early Experiences and Lessons Learned

When I first started beekeeping, I adopted the standard practice of frequent hive inspections and periodic varroa testing using the sugar-roll method. In my first year, by mid-summer, the mite count in at least one hive reached the usual treatment threshold (around 3% infestation). I waited for the right weather conditions and used a formic acid treatment, which resulted in a noticeable number of dead mites on the bottom board. I felt relieved, believing the treatment had been successful.

But when winter drew to a close, one of my colonies had perished. A closer inspection suggested varroa mites had overwhelmed the hive despite the summer treatment. The second colony did survive, but I was frustrated by the loss.

In year two, I replaced the lost hive with a new bee package and repeated a similar routine: regular inspections, regular mite checks, and another organic product (this time based on hops beta acids) when mite counts hit the 3% threshold. Unfortunately, both colonies died that winter. Determined not to give up, I spent the off-season researching varroa mite biology, speaking with entomologists, and attending specialized talks at beekeeping conferences.

From all that study and conversation, I concluded one vital fact: no matter how carefully you monitor, mites are always a threat, and you can’t rely on just a single mid-season treatment to keep them under control.

A New Perspective on Varroa Management

After digging into scientific papers, talking to experts, and reviewing anecdotal experiences from veteran beekeepers, I put together a more proactive, season-long plan—one that might be considered unconventional or “off-label” because it involves monthly oxalic acid vapor (OAV) sessions as a “knockdown” procedure, followed by a longer-term treatment in late summer or early fall. Below is a snapshot of the disclaimers and objectives before outlining the plan:

1. Small-Scale Focus: I manage only a handful of backyard hives, not a commercial-scale operation.

2. Survival First: My top priority is to keep my bees alive through winter, even if it means fewer honey supers on the hive.

3. Non-Traditional Approach: The method uses OAV monthly during the active season, which isn’t a standard recommendation for varroa control.

My Monthly OAV “Knockdown” Schedule

Here’s the monthly plan I follow, adapted for a climate similar to Colorado. Depending on where you live, you might adjust specific start times:

1. No More Mite TestingI’m well aware mites are present—even if I don’t see them. Instead of waiting for a threshold, I assume I need to keep the pressure on year-round.

2. Monthly Oxalic Acid Vapor Treatments

   • Existing (Overwintered) Hives: Start around May.

   • New Hives or Splits: Begin in June or July.

   • Frequency: Perform OAV once a month, up until the first or second week of August.

   • Honey Supers: Temporarily remove supers during the 15-minute vaporization process, then place them back on immediately afterward.

3. Long-Term Organic Treatment in Late Summer

   • Timing: After the final OAV knockdown (late August or very early September), remove honey supers for harvest.

   • Treatment Options: Use a multi-week product like thymol (e.g., Apiguard), formic acid strips (e.g., Mite Away Quick Strips), or hops beta acids (Hop Guard II). This extended treatment targets mites in capped brood and provides added protection going into winter.

Stunning Results

The first time I followed this monthly regimen, three of my colonies made it through winter—including one that had seemed weak going into the colder months with only one deep of bees. By spring, my healthy colonies were strong enough to split, and one even swarmed (which I managed to recapture).

The following year, I repeated the same approach with four hives. Once again, all four survived winter. Two were split in spring, and the others built up quickly enough to fill supers with honey by early May. Since adopting this proactive monthly OAV schedule, my colony losses have dropped to zero—and I’ve been able to expand my apiary substantially.

Frequently Asked Questions

1. Why Treat with Oxalic Acid Vapor in Summer When It Doesn’t Penetrate Capped Brood?It’s true OAV isn’t as effective once mites are sealed in brood cells. However, I’m not relying on it as a standalone, full-coverage treatment. Instead, it’s used as a periodic “knockdown” that significantly reduces the number of phoretic (adult) mites. Even if 30-35% of mites are wiped out in each monthly session, that constant culling slows population growth until the more thorough treatment in late August or early September.

2. Can I Use OAV with Honey Supers On?Generally, no. I quickly remove the super right before I vaporize and set it aside. Most adult mites are on bees in the brood boxes, so missing mites in the super frames isn’t a big concern. After about 15 minutes, the treatment ends, and I put the honey super back in place.

3. Aren’t You Worried About Mite Resistance or Harm to Bees?Varroa mites have shown resistance to certain synthetic treatments, but evidence so far suggests they don’t develop resistance to oxalic acid. Most research also indicates oxalic acid vapor is relatively safe for adult bees when used correctly. My colonies have thrived under this regimen.

4. If I Don’t See Mites, Should I Still Treat?Absolutely. Varroa spreads easily through drifting drones, foraging on shared flowers, and robbing events. Even a single mite that enters your hive in early spring can multiply exponentially by fall. Regular treatments keep their population from exploding, safeguarding your colony’s health.

Final Thoughts

While there’s no single “magic bullet” for varroa control, this monthly OAV knockdown plus a long-term organic treatment has been a game-changer for my hives. By accepting that mites are always around—and acting accordingly—I’ve kept my colonies thriving and avoided the heartbreak of multiple winter losses. If you’re looking for a fresh approach to varroa management, consider giving this plan a try, and remember to adapt timings based on your own climate and hive conditions.

What’s your experience with oxalic acid vapor or other varroa treatments? Feel free to share your thoughts and questions in the comments below!

Additional Resources

• Explore oxalic acid vaporization research from university beekeeping labs.

• Check label instructions for any treatment product you use to ensure it’s applied safely and effectively.

• Collaborate with local beekeepers to coordinate treatments and reduce mite reinfestation across nearby colonies.

Oxalic Acid Vaporization

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