OAV Varroa Mite Treatment: Ask the Expert!

OAV Varroa Mite Treatment: Ask the Expert!

Josh Vaisman replies to questions from his article: How to Treat Varroa Mites with Oxalic Acid Vaporizer (OAV) “knockdown” treatment:

Jim writes:
I loved your article on monthly knockdown mite treatments using oxalic acid vapor. I live in Indiana with summer temperatures reaching 90+ sometimes often. In your article, you mentioned no temperature limits with OAV unlike the limits with MAQS. My question, is there any high temperature you would not apply a summer treatment?

Thanks for your kind comments about the article on monthly knockdown mite treatments — and thanks for the question!
The simple answer is, no, there is no upper ambient temperature above which you should not use OAV.  That’s another wonderful benefit of OAV.  
Where I live, in Colorado, we regularly have days above 90 (sometimes even 100) degrees during the peak of summer. This is precisely the time I want to knock down the mite population and most other treatments are not feasible to use.
That said, the bees aren’t necessarily fond of being stuck inside a hot hive for very long. So I recommend you follow the OAV instructions for as long, and only as long, a time period as necessary. As you know, you’ll need to seal the hive for the treatment. Just be sure to “unseal” the hive as soon as the treatment is completed.
For what it’s worth, I have seen recommendations for a lower ambient temperature limit. As you can see HERE Dadant suggests only using OAV when the air temp is above 37 degrees.
I hope this helps.  Let us know what other questions you may have.
All the best to you!
– Josh 

Annie writes:
Why can’t I just use formic acid strips in July and again in Sept? As I understand it, this is an organic option and kills the mites inside the brood cells as well. Also with a top bar, can I just place the strips on the top under the roof? Will it permeate below? Otherwise, I place them below the bottom mesh and seal it up.

Josh replies:
Some great questions, Annie! In regards to your first question you could absolutely use formic acid strips like Mite Away Quick Strips in mid-summer and again late-summer/early fall. The primary takeaway should be that a fall treatment alone isn’t enough to sufficiently control the mite population so a mid-summer treatment is preferred. That said, MAQS is highly temperature sensitive, which can make summer usage a challenge, depending on where you live. For example, the first 24 hours the strips are in the hive cannot exceed 85 degrees. The next 3 days cannot go over 92 degrees. In Colorado, where I live, it can be difficult to find a week like that in June or July. Oxalic acid vaporization, however, does not have the temperature restrictions. That said, it isn’t quite as effective as MAQS, which is why we choose to do a single “knockdown” vaporization once a month through the summer. On the flip side (once again!), MAQS has some risk to it in that it can harm some brood and, in rare cases, result in queen death. OAV does not seem to have the same risk.

In regards to your second question about using formic acid strips in a top bar hive, the company the instructions that come with MAQS from the manufacturer only refers to use in Langstroth hives. That said I have heard of Top Bar Hive beekeepers using MAQS as you suggested on top of the top bars themselves. I can’t tell you how effective it is, though. My suggestion would be to find an experienced TBH beek in your area (maybe your bee club?) who can help guide you there.

Josh Vaisman, Backyard Beekeeping Expert 


Skye writes:
What do you recommend for top bar hives where you cannot move supers aside?

Josh replies:
Skye: Thanks for the question! So, the rule is, according to the US Environmental Agency (who approves all mite treatments for beekeepers), the only mite treatment that can be used with comb intended for honey consumption is Mite Away Quick Strips. For every other treatment – organic or not – we are not allowed, legally, to consume or sell/give away the honey that was exposed to the treatment.

Now, I’m not a Top Bar Hive beekeeper so my experience with TBH is limited. But I wonder: Is there a way you can remove and set aside the bars with the honeycomb you intend to consume and run an OAV treatment in the hive? The OAV treatment takes 15 minutes and you could just put the bars with that comb back in the hive after. This is what we do in the summer — we pull the super, including all the bees inside, and set them aside. We then seal up the hive (so it’s just the boxes of brood) and run our OAV knockdown. Once the 15-minute treatment is over there is no more OA vapor inside the hive and we put our super right back on and go from there.

I hope that helps!


Mike writes:

Congrats on your success, going into winter, how exactly do you set up your hives and when do you do the steps? I’ve tried many ways here in Pittsburgh — insulation, ventilation boxes, sugar boards, you name it. I might have tried it. I lost three of my four hives late spring this year. I would really like to try your set up. I’ve been making OAV treatments every month this year without checking mite levels. The one and only hive I have this season always has high mite kills on my screen bottom insert, just finished a four-week treatment and still can’t knock them down. I had one hive once that after the first treatment, they went mite-free totally, the only time I ever had a hive without mites. Turned out the hive was bloodless, the queen wasn’t laying. So if you ever have a hive with no mites you can bet there’s a queen problem. 

Josh replies:
Hey Mike! I’ll do my best to explain our hive setup – please let me know if I miss something or you have any further questions. So, we use Langstroths in 10-frame configuration. Our hives sit on screened bottom boards and are stained, not painted. When we build equipment, if we have propolis around, we make a propolis tincture (mix strong alcohol with propolis in a jar and let it sit, in the dark, in the house, for a week or two), scrape the inside of the boxes so they are rough inside instead of smooth, and “paint” a thin layer of the propolis tincture on the inside of the boxes. This is only for the deep boxes that will be used for brood chambers and we make sure to let them air dry for at least a couple days before bees go inside them. All our hives overwinter in a three-box configuration – 2 deeps and a medium super. Our intention is to give them “extra” honey for the winter. For our overwintered colonies, we begin monitoring hive weight in Feb/March on a typical year – earlier if it was a warmer than normal winter. And we feed them as needed whenever it is warm enough. 1:1 sugar water. In mid to late March, we start our swarm management. That is, if the cluster has moved up in the hive, we’ll take the bottom (now “empty”) box and rotate it to the top of the hive. When we start seeing drones from all our hives, we begin making our splits. Now our goal is to make sure they are all queen right, they have enough food, and they are building up in population. Starting June, usually around the 1st, we do our fist Oxalic Acid Vaporization knockdown to all our hives. If we made splits and we are comfortable they are well on their way we will OAV them too – but only if they have a healthy, laying queen and lots of brood. From here on out it’s monitoring queen and colony health and monthly OAV knockdowns. Our big nectar flow usually starts somewhere in June so we start putting supers on them. Where we live a strong colony will fill around four supers in a season, maybe five. Around the 3rd or 4th week in August, we pull all our supers, except for leaving one for the bees, and then start our fall full mite treatment. In the past, we’ve done a 2-dose treatment of Api Guard, MAQS, or Hop Guard II. Once the temperatures are regularly below about 50 degrees for a high (usually November-ish) we wrap our hives in a Bee Cozy and reduce the entrance as well as put the slider in the bottom board to close up the screen. Oh, one more thing, we elevate the front of our outer covers all year round to maximize upper ventilation. This also serves as an upper entrance for the bees. I hope this helps! Let me know what other questions you may have.


Friend O writes:
I am a little confused. The article seems to address May through the beginning of Sept. I’m not clear what is being done the other months. Can anyone help me with that?

Josh replies:
Happy to help, Friend O! We live in Colorado where the active bee season, in a typical year, begins in March and ends around September/October. By active I mean the period of time the queen is laying in such a way to INCREASE the size of the colony. The months of October/November through January/February, in Colorado, the colony size is either shrinking or remaining the same as the natural resources are limited or totally unavailable. As such, the mite population begins growing around March and begins shrinking or plateauing around October/November. To that end, we only manage the mite population during the active season. So long as we keep the mite populations in our hives minimal during the active season our bees do quite well, without mite intervention, through the winter months. I hope that helps clarify things for you!


Josh Vaisman is an avid beekeeper and instructor in Northern Colorado. An active member of the Northern Colorado Beekeepers Association, Josh has been involved in the education of new beekeepers on behalf of the association and privately. Like most people who study apiculture, Josh started into beekeeping as a hobby, and offers valuable experience to those wanting to start beekeeping about the learning curve involved, what to do, and what not to do when getting started. When not tending to his hives, Josh is a Positive Change Ninja with Flourish Veterinary Consulting, a company he co-founded to apply the science of well-being to the veterinary workplace. He lives in Firestone, Colorado with his wife, Greta.

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