OAV: How to Treat Varroa Mites

OAV: A Varroa Mite Control and Treatment Plan That Works

Promoted by Miller Bee Supply
OAV: How to Treat Varroa Mites

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My wife and I took a beginning beekeeping class before becoming backyard beekeepers. We learned about wax moth treatment and how to manage ants in beehives. We also learned how to treat varroa mites. We learned that around 30-40% of bee colonies in America do not survive each year so we started with two hives.

In this article, I’ll discuss our experience trying to manage varroa mites our first couple years in beekeeping, some lessons we learned, a new way of approaching varroa management, and address some common questions about our management plan.

After getting our bees, we began a monthly mite testing regiment using the sugar roll method. In July, the test suggested we had reached three percent mite infestation so we knew it was time to treat. We waited for a week with appropriate temperatures and applied a formic acid treatment. By the end of the varroa mite treatment, we found TONS of dead mites on the bottom board and we felt pretty good about how things had gone.

A section of the bottom board slider after a varroa mite treatment … covered in dead varroa!

Late that fall, after Thanksgiving, one of our colonies perished. An “autopsy” suggested they had succumbed to the cumulative effects of varroa mites. The other colony survived the winter.

Our second year we bought another package of bees to replace our lost colony and went about our beekeeping how we had been taught — regular inspections, regular mite testing, organic treatment when mite loads reached 3 percent. This time we used a hops beta acids treatment and saw many mites had been killed by the treatment.

Neither of our colonies survived the winter our second year. We were very discouraged and used our sadness as motivation to learn all we could about varroa and varroa management. We read every scientific article we could, spoke to entomologists and other bee researchers, and attended lectures at bee conferences focused on varroa mites. Based on all of the above we came to accept the following varroa mite facts:

With this in mind, we developed a plan for managing our hives. Before sharing our plan and its results, I’ll offer some disclaimers:

  • We are backyard beekeepers who manage between two and seven hives. We are not large-scale beekeepers.
  • Our varroa management style is non-traditional and would be considered “off-label.”
  • Survival of our bees is our primary goal — honey harvest is secondary.

Varroa management plan for Colorado and similar climates:

  1. We have stopped testing for mites. We know they are always there.
  2. Monthly single oxalic acid vaporizer (OAV) “knockdown” treatment. For overwintered bees, start in May. For new hives, start in June or July. Repeat monthly with final OAV treatment in the beginning to middle of August.
  3. If honey supers are present, remove supers during treatment and replace immediately after treatment.
  4. Remove honey supers at the end of August or very beginning of September.
  5. Apply a long-term organic mite treatment after removing honey supers. Examples would be Apiguard (thymol), Mite Away Quick Strips (formic acid), or Hop Guard II (hops beta acids).

We began this regiment in our third year. The results were stunning.

Our three hives overwintered including a colony that had struggled all summer and entered winter with only one deep of bees. Our two healthiest colonies were easily split in the spring and one swarmed as well (we caught the swarm).

We repeated our varroa management plan in year four with equally impressive results. All four hives overwintered. From two colonies we were able to make three spring splits. A third colony we provided a third deep to expand into and our fourth hive swarmed. All four colonies were full of bees by the end of April and producing honey in supers by early May.

We began this varroa mite management plan two years ago with three beehives. In those two years, we have not lost a single hive — all of our bees have survived and, from those three original colonies we have produced seven additional hives! We have finally figured out how to treat varroa mites!

Some Common Questions That We Are Asked:

I thought OAV was not effective in the summer? Doesn’t it need to be done once a week for three weeks?

OAV is not an effective treatment during heavy brood-rearing periods since it does not penetrate capped brood. However, we are not using it as a full treatment. We are using it as a mite control method we call a “knockdown.” That is, we simply want to significantly reduce the number of mites in the hive.

OAV is very effective against phoretic mites. We estimate this “knockdown” eliminates between 30-35 percent of mites in the colony. This assumes between 35-50 percent of mites are phoretic and the single OAV kills between 85-95 percent of the phoretic mites.

A hive sealed during an OAV treatment.

Isn’t it true you can’t do OAV when honey supers are on?

Yes, it is true. We remove our honey supers during the monthly OAV knockdown and set them aside. The vast majority of phoretic mites are on bees in the brood chamber so we aren’t concerned about missing a lot of mites. Also, the OAV treatment takes about 15 minutes so we set the super aside while we treat the hive and then replace the super when we are done.

Are you worried about overtreating? Mite resistance? Hurting the bees?

All the current research suggests mites do not develop resistance to OAV. Furthermore, research suggests OAV has little to no harmful impact on bees. Our subjective experience these past two or more years seems to support this.

But I don’t see any mites. Are you sure I should treat?

All the research strongly suggests every colony has or will have mites. This is because of natural drift. Mites prefer drones and drones are able to move uninhibited from hive to hive. Furthermore, bees from several colonies in an area forage on the same flowers and mites have been shown to move from bee to bee during foraging. And mites reproduce prolifically — one mite in January could mean over 1,000 mites or more in October.

We believe no matter what we do we will always have mites. Our goal is to keep their numbers as low as possible to provide our bees the best chance to thrive.

Now that you’ve learned about our philosophy and management style for varroa mites, what questions do YOU have?


See what other beekeepers have asked about OAV treatment and Josh’s answers in our Ask the Expert section.

8 thoughts on “OAV: How to Treat Varroa Mites”
    1. Thanks for sharing?
      Question, have you used the OA in the fogger?
      Do you know about the thermal hive approach, where the hive is heated to 106 degrees for 90 minutes, this method is reported to also kill mites in the brood?

      Great article, the word needs to get out.
      Good job
      919 274 5558

  1. HI,

    thanks for a great article. What time of day is best to treat OAV? My guess is late evening when most foragers are home, but you haven’t said.


  2. Josh Thanks, I had just come to this conclusion. And your Great article confirms that to me, I am right. I would like to ask what time of the day do you think is best to apply the OA? Where could I go to print this out? Do you have a more in depth article on this? Thank You so so much, can’t say this enough, love my bees. Sandy Pruett

  3. Problem: My bees were delivered in June, almost a month past their promised date, and I had one day before a flight to California. I had prepared two new supers, one empty of frames – figuring the bees would come with 8 frames in their box. Wrong. 5 frames and I didn’t have any extra. So I put sugar water and two brood patties under the cover – and left for a week. I thought they would build comb on the frames in the other, bottom super. Wrong. They filled up the empty frames space. I returned to find a huge hanging comb that fills the empty space. Since I returned I have thought a lot of what I could have done. But now my question is what can I do without destroying the brood?
    I’ve had bees in up state NY and my hives there survived ice storms and bear attacks now I live in Oregon.

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