Inside: Disposable shop towels soaked in a mixture of oxalic acid and glycerin may be the next reliable varroa mite treatment. It’s cheap, fast, and effective.
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For beekeepers who treat beehives for varroa mites, oxalic acid has become the default favorite miticide. Oxalic acid is inexpensive, a natural component of honey, safe for bees when used as directed, and 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 works 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 beekeepers, 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 for the mixture
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 die 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 have to re-enter the hive to collect them. It’s the closest thing to magic I’ve seen in a while.
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 are 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
- Heat-proof 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 Randy prepared the shop towels
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.
- Wear chemical-resistant gloves and protective goggles when using oxalic acid.
- Use 25 ml of glycerin, 25 grams of oxalic acid, and one shop towel for every hive.
- Stack the shop towels in the plastic tray.
- Heat the glycerin in the microwave until hot but not boiling (about the temperature of a cup of coffee).
- Stir the oxalic acid into the warm glycerin, mixing thoroughly.
- Pour the warm mixture over the towels in the tray.
- Once saturated, Randy moved the towels to the second tray to drain. He 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.
- Store the remaining liquid in a glass jar for later use. Randy warns that the liquid became quite blue.
Once ready, Randy 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.
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