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Oxalic acid and glycerin for varroa mites

For beekeepers who treat for varroa mites, oxalic acid has become the default favorite miticide. It is inexpensive, a natural component of honey, safe for bees when used as directed, and is drop-dead effective. But being beekeepers, we can’t agree on anything, so the disagreement about how to apply oxalic acid rages on.

The US Environmental Protection Agency (EPA) currently recognizes three ways: spray, dribble, and vaporization. The spray method is often used on packages, but disagreement about dribble vs vaporization for complete colonies continues to fester. Being fundamentally a minimalist, I prefer the dribble method (less equipment, less expense, less danger) but each time I say so, I get trounced by those who thrive on great clouds of toxic fumes. Whatever.

Randy Oliver to the rescue

But now, biologist Randy Oliver offers us hope in the form of a disposable shop towel soaked in oxalic acid and glycerin. In fact, I have received so many questions about Randy’s new system, I’ve decided to write a short summary of his findings. However, I highly encourage you to read his paper in full, which details his methods, results, and statistical analyses. It also contains many photos.

The original idea for dissolving oxalic acid in glycerin came from elsewhere, but Randy took the idea and refined it. He tried various methods of delivery to find the one method that would be safe for bees and beekeeper, deadly to mites, and both economical and quick. So far, his new method has exceeded his expectations and, much to his credit, Randy is now working to get the method endorsed by the EPA.

The basic idea

The original research showed that dissolving oxalic acid in glycerin provided a way to slowly release the oxalic acid over time. Unlike dribbles or vapor where the dose is applied all at once, the oxalic/glycerin mix provides a slow release that is remarkably effective against mites but easy on the bees. Randy has been able to extend one treatment to last about 30 days, which means multiple treatments are not necessary. Mites are killed as they emerge from the brood cells without repeat applications.

Randy has amazing photos of his bees raising brood all around the soaked towels, seemingly unaffected by their presence, yet the mite kill is spectacular. After about 30 days, the bees have removed the entire towel from the hive so the beekeeper doesn’t not have to re-enter the hive to collect them. It’s the closest thing to magic I’ve seen in a while.

What is oxalic acid?
Oxalic acid is a naturally-occurring organic compound. In its pure form, it is a colorless crystalline solid that dissolves in water. Many foods contain oxalic acid, including buckwheat, parsley, rhubarb, spinach, beets, cocoa, nuts, berries, and beans. In industry, oxalic acid is often used as a cleaning or bleaching agent.
What is glycerin?
Glycerin (or glycerol) is a sweet, non-toxic colorless and odorless liquid. It is widely used in both the food and pharmaceutical industries for a variety of purposes, including as a binder, thickener, sweetener, solvent, and humectant (a product that retains moisture). It is typically derived from soy or palm but can also come from tallow.

The supply list

Here are the supplies used in the experiments. Some are listed in the article and some I assumed. Plastic, glass, or wood utensils would be necessary since metal can be ruined by oxalic acid.

  • Oxalic acid dihydrate (wood bleach)
  • Food-grade glycerin
  • A flat plastic tray for soaking the towels. Randy recommended two 12 x 14.5 x 2-inch InterDesign Refrigerator and Freezer Storage Organizer Trays.
  • Blue disposable shop towels. The article doesn’t specify a brand, but Randy says his towels fit nicely into the above trays. Looking over various offerings, I found that Scott 75143 Original Shop Towels are 11 x 13 inches, so I assume something about that size would work.
  • A scale for weighing the oxalic acid
  • A glass measuring cup for measuring and heating the glycerin and mixing in the oxalic acid
  • A plastic or wooden spoon or spatula for stirring
  • A glass jar with a plastic lid for leftover solution
  • Chemical-resistant gloves (nitrile)
  • Protective goggles

How the shop towels were prepared

Randy is quite clear that he is still refining the method, but here are the steps that worked for him in his summer hives. Testing on winter hives is still underway.

  1. Chemical-resistant gloves and protective goggles are needed when using oxalic acid.
  2. He used 25 ml of glycerin, 25 grams of oxalic acid, and one shop towel for every hive.
  3. The shop towels were stacked in a plastic tray.
  4. The glycerin was heated in the microwave until it was hot but not boiling (about the temperature of a cup of coffee).
  5. He stirred the oxalic acid into the warm glycerin, mixing thoroughly.
  6. The warm mixture was poured over the towels in the tray.
  7. Once the towels were saturated, he removed them to the second tray to drain. Randy says, “Squeeze or press them until you’ve recovered half the solution.” This is important for achieving the proper dose and encouraging the bees to remove the towels.
  8. The remaining liquid can be stored in a glass jar for later use. Randy warns that the liquid became quite blue.

Once the towels were prepared, he placed one towel across the top bars of the lower hive body of each hive.

Be sure to read the whole article

Remember that this post is my interpretation of what Randy wrote. Be sure to read his .pdf for all the nuances that I may have left out. Also remember that this method is not yet approved by the EPA and is therefore illegal.

Rotate Your Treatments
Like any other mite treatment, oxalic acid must be rotated with other treatments to prevent or delay resistance. Reports that mites are somehow unable to develop resistance to oxalic acid are completely unfounded.

Rusty
Honey Bee Suite

Varroa mite
Varroa mite. Pixabay photo.

Note: this post contains affiliate links.

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Comments

Oliver
Reply

We know this treatment making stripes using cardboard for many years, comes from Argentina Mr.Prieto of apiary Los Alamos, the queen breeder of famous NAVEIRO line, invented this form.

Resistance against ACID is nearly impossible. Only if mites getting a grosser shield. But this never could be observed in the past.

Rusty
Reply

Oliver,

Yes, resistance to acid is nearly impossible, but we don’t yet know if the mode of action is pH or if it is something else. Many beekeepers assume that it is just the pH, but assuming is not knowing. Until we know for sure, the precautionary principle is advised.

Wei
Reply

I wonder if perhaps this method could be used when the honey supers are still on then perhaps?

Rusty
Reply

Wei,

I doubt that warning will change unless someone is willing to pay for studies.

Carol
Reply

Rusty, this is fantastic! Thank you for sharing it. I will definitely read Randy’s write-up.

Laura Colburn
Reply

Hi Rusty,
You end with a note saying, “Reports that mites are somehow unable to develop resistance to oxalic acid are completely unfounded.” Have you come across any reports indicating resistance? I’ve been searching the internet for data on that very topic and haven’t found much.

This new method Randy Oliver is trying is intriguing. I’ve downloaded his article and look forward to reading it. I’ve been fortunate to hear Dr. Rangal and Liz Walsh both present their findings on the effects of miticides on queens. Liz doesn’t seem to be a fan of oxalic acid, so I’m hoping the A&M Honey Bee Lab will be able to include research on it in the near future.

Thanks for keeping us informed on the latest in our battle against Varroa.
Laura

Rusty
Reply

Laura,

No, I haven’t read of any pockets of resistance. But OA treatments weren’t legal in the US until recently, so they weren’t widely used. As more and more people use them, the selective pressure will increase. One problem in particular is that we don’t know the mode of action of OA in varroa mites. Some people think it’s merely the pH, but others think it’s more complicated. Until we know, it best to operate on the safe side and use the precautionary principle.

frances I Moore
Reply

Rusty can u or someone convert 25 ml to us measurments and what would 25 grams be is that tablt spoon cup i can not find the answer on the web thanks

Rusty
Reply

Frances,

It’s easier to just use a measuring cup and scale that has metric measurements. Many have both scales on them. 25 ml is about 5 teaspoons. 25 grams is a little less than an ounce by weight. But you don’t want to get this wrong or you could end up hurting your bees. You can get a scale that measures tenths of grams for less than $10 on Amazon.

frances I Moore
Reply

Thanks for everything, u are great, keep the post coming I so much enjoy them.

dave hortin
Reply

I bought my digital scale at Smith & Edwards in Far West (my second one anyway, my first from a smoke shop) and got my syringes (free) from Walmart Pharmacist for the 25 ml ( about #/8′ diameter by 3′ long) mixed in styrofoam cup ( or glass I’m told) in microwave for 30 seconds (on high), then dribbled on blue shop towels, then placed in ziplock baggies until I could get bee suit on (and get my courage up) then placed on top of my two hives and left there for 10-14 days then removed during next hive inspection. good luck. mixed up on 5-29-17, & placed on hive frames, removed on 6-10-17. i plan on doing a powdered sugar mite count (w/ assistance of Utah state dept. of Agg. bee inspector-of course) next weekend (7-1-7/4) hopefully get low mite counts…

Wei
Reply

Dave,

I think I see a flaw in your timing/application of the OA. My understanding of the towel method of treatment is to allow for longer slower release of the OA into the hive as opposed to the one shot deal with vaping. If your removing the towel after only 14 days, I think your missing part of the benefit from applying through this method. As is, I think most people using the vapor method apply three times 7 days apart in order to get all the capped brood but if you removing he towel after 14 days, aren’t you missing some brood? The method with the towel was also meant to have the bees chew and remove the towel over time which allows for the slow release and disbursement of the OA brood emerges as opposed to you removing the towel yourself. If you read the article, Randy goes into great length in finding the right proportion/consistency of the towel in order for the bees to be able to chew up the towel themselves.

Rusty
Reply

Dave,

Wei is correct on this and makes some good points.

Paul
Reply

Hi Rusty! Another wonderful article!! Thank you! I’m lucky enough to live close to Randy Oliver and my local beekeepers association is offering an advanced beekeeping class in April that will be taught by him and which I will be attending. If his OA method isn’t part of the class I will be sure to ask him about it.

Dan Stoffel
Reply

Presenter wasn’t quite clear—did he use one shop towel per brood chamber or one towel per hive (2 brood Chambers)?
Having been a research Biochemist, I truly appreciate the amount of effort that went into this research, Kudos to Mr. (Dr.?) Oliver and his crew.
Thanks,

D. Dtoffel

Rusty
Reply

Dan,

(Mr.) Randy used one towel per two chambered colony and he put the towel between the two chambers.

Graeme
Reply

Thanks Rusty, that’s very interesting.

I’m based in New Zealand and we are coming out of the worst season in 2 decades, almost no stores let alone excess honey, will be a long winter 😡

However varroa has flourished this season so I’m keen to try this, but am trying to work out what a shop towel equivalent is here, are they a thick paper towel or an actual fibre towel? This is all I can find http://www.supercheapauto.co.nz/Product/SCA-Shop-Towels-200-Pack/376538, should work ?

Rusty
Reply

Graeme,

Your source seems to be a little larger, but I think they would work. Shop towels are often sold in automotive stores, so that sounds right, too. They are like a strong and thick paper towel. And if you wanted to cut them a little smaller, you could.

debbie
Reply

WOW … what a brilliant idea ! Thanks for sharing.

Cathy Wilde
Reply

Rusty, I can’t thank enough for your blog. It has been a constant source of wisdom, perpective, comfort, and chuckles. And this … this is exciting stuff! I’ll be trying it this summer for sure! Thank you again for your great service to bee-kind.

Rusty
Reply

Thanks, Cathy.

Mark
Reply

Hi Rusty,
Can you please comment on using OA in regards to harvesting honey. Is there a specific time to wait once the treatment is completed before you can remove honey safely from the hive? What would be the best time frame (what months) for treating a hive so you can harvest honey?
Thanks very much,
Mark

Rusty
Reply

Mark,

The EPA label is the law. It says, “Do not use when honey supers are in place to prevent contamination of marketable honey.” Since it says no more, I assume you can apply supers as soon as the treatment is complete. The best time to treat is going to vary depending on where you live. I generally have my supers off buy the end or June/first of July, but things may be different in your area.

Cathy
Reply

Thank you
I’m trying this
Lost my hives the last 2 years in the fall from mites

David
Reply

In previous oxalic vaporization, it was necessary or suggested to remove the honey supers or place a barrier between the brood nest and the honey supers. After reading Randy’s information, I didn’t see any reference to this in this new treatment. Can this new method be used while honey supers are on?

Rusty
Reply

David,

Because no difference was mentioned, I would assume the safety measures would remain the same. That is, I would use this method before or after honey supers.

Tom Mckinney
Reply

Thanks for the great info Rusty. Will put this method to work when season gets underway.

Fred
Reply

Rusty,

Very interesting article. Certainly sounds like a promising safer way to treat for the mites.
I would only caution one thing. You mention the glycerin should be hot but not boiling. That leaves a lot of room for interpretation, as the boiling point of glycerin is around 554 degrees F. A different way of putting it would be to use a thermometer and a specified temperature range.

Very interesting article.
Fred

Rusty
Reply

Fred.

Hmm. Good point. I added Randy’s description to the post. He says to heat the glycerin until it’s like a cup of hot coffee. That would be a bit less than 554 🙂

Shawn Bird
Reply

Graeme,

A shop towel is simply a very strong, fibrous paper towel.
I’m interested in the method of draping the towel. I’m a TBH keeper and this method could easily be adapted to drape over a bar holding brood comb.

jim
Reply

Great information, Rusty. This could be a really useful way to apply OA in a single treatment. I haven’t heard of this before

Jim
Reply

Rusty,
Thanks so much for bringing this article to our attention. I am also from NZ and presently use OA vapour treatments and see this as an alternative to that. I lost all 4 of my hives to varroa infestation last year even with OA treatments – my problem though, not the OA. The varroa got way too far ahead of me to save the hives. So far this year I had to start is a queen cell and a shake of bees from a local beek. I am back up to 3 hives now, although we have had a terrible summer for the bees this year. Thanks again for our website and your time creating and collating all this good information. Cheers!

Cal
Reply

If one looks at Mr. Oliver’s article, which I’d encourage anyone wanting to know the specifics of his technique and its development to do prior to using it, it’s evident that strips hung between the frames as the Argentinians did produced a somewhat longer-lasting effect than his shop towel method. The driving force behind using shop towels laid across the top bars was good effect with maximum convenience, as there’s no need to reenter the hive to remove anything; the bees take out the trash. Making the OA/glycerin solution involves heating the mixture to 150 degrees Fahrenheit and holding it near that temperature for several minutes until all the OA has dissolved. Esteban, on the TECA site, describes a 60% w/v solution, Maggi, et. al., in their paper describe a 33% w/v solution, and Oliver describes a 50% w/v solution in his ABJ article. Glycerin is flammable and OA is dangerous. Don’t overheat the mixture trying to dissolve it; take your time. Don’t heat it directly over a flame or heating element. Don’t heat it in metal or plastic. I used heat-proof glassware and a water bath (large Pyrex measuring cup set in a few inches of water in a crockpot on high). Wear chemical resistant gloves such as you can find in the hardware store and use goggles. Glycerin can pass through your skin, so immediately rinse it off well if the solution gets on you. If it has OA dissolved in it, you may get a nasty chemical burn and/or suffer OA poisoning or kidney damage. Having a jug of water with a good quantity of baking soda dissolved in it to use as a neutralizer if the OA/glycerin gets on your skin, as Mr. Oliver recommends, is a smart idea. The effectiveness of OA seems to be related to getting it on the bees where it can damage the mites. The other application methods do this, whether via a fog condensing on everything in the box (heated vaporization) or dribbled in sugar syrup. Esteban and Oliver both note that the paper fiber carrier has to be superficially “dry”, not with excess liquid on the surface, or the bees avoid it and then it has little effect. Drywall shim strips might make a good carrier if one wanted strips.

Oliver
Reply

Cal, you don´t need to heat the acid, I never did it, no need for it.
Oxálic heated too much will transform in formic acid (gas!!!!) that´s why it correct to warn from heating the acid.

Oliver
Reply

Rusty, USA is lightyears behind Europe in Varroa treatment. There they use the acids for decades and no resistance was observed. I think we can forget this point. More interesting is the correct use of treatments. A suisse study shows that the maiority of losses occurs with hobby and small beekeepers, professionals haven´t high losses caused by varroa.

Rusty
Reply

Oliver,

Did you read Randy’s article? I think not.

Oliver
Reply

Sure, and we use and study this method for years.

Mary Keogh
Reply

Ìs OA safe for the bees to eat as they chew on the paper towel?

Rusty
Reply

Mary,

The don’t eat it. They rip the paper apart with their mandibles and dump it outside the hive.

Bob
Reply

Hi Rusty,

I may have overlooked it but does this method discuss the application in a top bar?

Rusty
Reply

Bob,

I would just lay the towel over the top bars if you have room, otherwise I would drape it over one of the bars and let it hang down on either side.

Bob
Reply

Ok so at the risk of being annoying….if I just lay it across the top will the vapor just go up and out rendering it ineffective?

Rusty
Reply

Bob,

It’s going to depend totally on the shape and style of your top-bar hive, since they are all different. My top-bar bees spend a lot of time in their attic, since that’s where their feeder is. I imagine that as they travel back and forth to the feeder, they will eat away at the annoying towel. But if your top-bar hive doesn’t work that way, you will have to do something different, like hang the towel over a bar.

Oliver
Reply

No vapor, cause here we use oxalic, not formic acid. To vaporize oxalic acid you need a heat source.

Dawn
Reply

Bob, this method relies on contact with dissolved oxalic acid (OA), not vapor. The glycerin is used to dissolve the OA and hold it within the paper towel. It may sublime very slowly, but you should perhaps think of this as an extended oxalic acid trickle, not a vaporization method. I think the only reason that Randy mentions using it in warm summer hives is not for vaporizing the OA, but rather because when the glycerin/OA solution cools sufficiently, it develops crystals – the OA comes out of solution potentially rendering it much less effective.

Bob
Reply

And by the way u r funny.

Graeme
Reply

Rusty, I made up a batch of the towels, was very easy, but what I found is that I left them for 2 days under pressure, found the oxalic had started to crystalise on the paper before I put it on the hives. Will see if that makes any difference, but they moved away from it initially but today were walking over it and seemed to be trying to chew the edges

Question is, is there a period that the towels can be stored for or should one make them up and put them on the hives pretty quickly , the paper didn’t seem to cover that.

Rusty
Reply

Graeme,

Randy does says the extra liquid can be saved, and somewhere else he talks about crystallization in cold weather (which is generally dry). And in another place he talks about the towels disintegrating if they soak too long. All in all, I think I would just make as many as I could use immediately and save the extra in a jar.

noreen
Reply

Please help opened my double brood yesterday.they have not been taking down the fondant but have a good honey store. Bringing in pollen also. Very worried at affected bees with v.mite damage. Is it too late to treat with OA?and are the towells used the tear off big rolls used for cleaning up in workshops? PlEAseHELp

Rusty
Reply

Noreen,

Have you sampled your bees to do a mite count? That would be the first step. Use a sugar roll or alcohol wash, and then you will know whether or not to treat. The oxalic acid and glycerin method is still experimental and not legally recognized, so another method might be better, especially if you are not experienced. But yes, the towels are the blue tear-off type used for auto repair, etc.

Julia
Reply

Hmmm…if you do not distribute your bee-related products, is use of the paper-towel method “illegal” or is it simply not EPA-approved?

Rusty
Reply

Julia,

I’m not sure how it works. Using some in-hive products, like antibiotics, is just plain illegal because the government is trying to prevent resistant organisms from developing. Oxalic acid is an EPA-approved product, but this method of application if off-label. Probably no one would object unless you tried to sell the product. Supposedly the question at hand is how much OA gets in the food supply. It’s a good question for a lawyer.

Clark
Reply

Hello there Rusty,

Just discovered Randy’s article last night – it looks promising! Thanks for your great article and being able to condense it all. I’m still not totally clear on how dry the shop towel should be after you press and/or squeeze out 1/2 of the solution. In his photos it appears that his towel are still damp when applied to top bars. Is it also possible to let the shop towels dry out completely or will that decrease their effectiveness?

Thanks,

Rusty
Reply

Clark,

At one point Randy says, “If allowed to air dry, [the towels] will be a little stiff. Once in the hive, they will quickly rehydrate, and the bees will get to work at removing them.”

Graeme
Reply

Some feedback on this method, it certainly works and side effect is it seems to kill wax moth larvae which is great for overwintering boxes, BUT

A lot of Beekeepers here in NZ tried it and found it works well between two brood boxes, single boxes and nucs seem to ignore it and it’s definitely a contact treatment from what we can see .

It also is not a rapid knock down treatment so hives with high mite loads need to be treated with formic or strips, we have had a number of losses when used as end of season treatment

View here is that it’s a great maintenance treatment if the mite numbers are not nearing critical stage already, so maybe 3-4 treatments per year vs the current 2.

Also may be worth using the strip method on nucs and single boxes for hobby Beekeepers who have a bit more time, it seems to work better as the bees are in contact with it a lot more

Rusty
Reply

Graeme,

That’s interesting. I’ve also heard that it wasn’t working well in nucs, but I hadn’t heard anything about singles. I’m planning on trying it on singles, so I will be extra alert to that problem. I wonder if the relative wetness or dryness of the towels has any bearing.

Graeme

If you look at Randy’s update on 12 Feb he seemed to place less onus on the dryness of the towel compared to his initial method, but I treated 12 hives with one batch of fairly dry towels with varying results, I think a single box with honey supers above would work, but seems easy for the bees to ignore if they are not forced to moved up and past it. We have had the worst season in most people’s memory so a lot of hives were fairly weak comparatively which could have been a factor

Be really interested to see feedback from your readers through a full season.

Great blog by the way.

Rusty

Thanks, Graeme. I will be sure to pay attention to the singles when I try this, and make sure they have something overhead.

Al
Reply

Thanks Rusty! This is a great article.

I have a fellow beekeeper, that uses sumac heads, in his smoker. He swears by the method, and then uses oxalic acid, just prior to winter. He is a firm believer in knowing your mite load, FIRST. That gives you a baseline, of where you are, for treatment.

He has convinced me to sugar shake mine.

So, now I’m somewhat educated to what my load is. But, I’ll probably give this a shot. Sounds promising. Al

Rusty
Reply

Al,

As I’ve stressed here hundreds of times, treating without knowing your mite load is unconscionable and leads to resistance. Also count first, treat later.

Clark
Reply

The rehydration in hive part made me think it can be applied either damp or dry. Am I correct in assuming this?

Clark

Rusty
Reply

Clark,

Yes. I believe that is correct.

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