Posts Tagged ‘Oxalic Acid’

If you have not read the previous post, please do so. This is part 2…

Before I continue writing, Oxalic Acid Vaporization (OAV) is not an approved miticide technique in the US and is considered off label usage. It has been used for years in Europe and in many countries is considered the primary treatment for Varroa destructor. There are numerous beekeepers in the US using this technique and the equipment for performing OAV is readily available from a number of sources. But it is not yet approved! I am not in any way suggesting you use this technique in your apiary. I am describing how I use this in my apiary. Additionally, OA is hazardous to your eyes and lungs. Proper protection is required when using the vaporization method.

What is it?
Oxalic Acid (OA) is an organic acid. Do not get confused by the word “organic”, all it means is there is carbon in the formula. This is not a certified organic treatment, though it is considered a “soft” treatment. Everything I have read–and so far experienced–claims it does not affect queens, brood, or bees. It is 70x more toxic to mites than bees and can be used as long as the temperature is over 40ºF. Tho’ oxalic acid is naturally found in honey, you should not treat with the supers on if you are selling honey. Remove the supers during the treatment and replace them later or put a physical barrier between the brood boxes and honey supers so the OAV does not reach the honey. Why add anything to the hive with the supers in place? BTW, OA is naturally found in spinach, Swiss chard, beets (root part), beet greens (leaf part), collards, okra, parsley, leeks, blackberries, blueberries, raspberries, strawberries, currants, almonds, tofu, soy products etc…

The Varrox® unit has battery cable clips at the end of a 6 foot cable.

The Varrox® unit has battery cable clips at the end of a 6 foot cable.

Choosing OAV
Please read Randy Oliver’s 2-part article about OA dribble and vaporization on his website, Scientific Beekeeping. Randy goes into such excellent detail it would be foolish for me to repeat it here and I would be plagiarizing his work if I did. Let me simply say after reading his articles, checking the scientific references and (gasp!) reading numerous conversations on Beesource forums, I decided the claimed results warranted trying the vaporization technique.

The Components

I purchased the Varrox® 12-volt oxalic vaporizer Randy recommended on his website. The cost was $165, including shipping. I also purchased a tractor battery at Home Depot for $49, a full face shield respirator at Amazon for $110 and what I believe to be the cartridges for the respirator for another $34. Add the $6 I spent on OA (purchased on EBay) and the total comes to $364. Pricey? Compared to the toll on queens and brood most of the other treatments cause, I do not believe so. Plus, how much is a viable hive worth today? All of the components are a 1 time purchase except for the respirator cartridges and the OA and will last for many years.

During OAV treatment

In progress. Battery, iPad with stopwatch, vaporizer in hive. Note : 3 pieces of foam keeps bottom entrance sealed. Middle piece is removed then replaced to insert/remove Varrox® unit


The key is to seal the hive so when the OA is heated, the vapors remain in the hive. All I did was close the upper entrance by pulling the outer cover tight across the front, place sticky boards under the screen bottom boards and stuff pieces of foam in the bottom entrance. The Varrox unit comes with spoons for measuring out 1 gram of OA. I use 1gr OA per brood chamber (2gr for my larger hives # 1 and 2 and 1gr for hives #3 and 4 ) and pouring it into the cup of the Varrox unit, I place the cup with OA  in the front of the hive through the bottom entrance, seal the entrance with foam, hook up the leads to the battery and wait 3 minutes. The Varrox unit vaporizes the OA which then fills the interior of the hive. A very small amount of vapor does come out of the hive. This is why I wear the face shield with respirator and use gloves. At 3 minutes I remove the leads from the battery and wait a couple of minutes for the Varrox to cool. I remove the foam around the unit (I use 3 pieces of foam so most of the bottom entrance stays sealed while I do this) pull the Varrox unit out of the hive, replace the foam and let the hive remain sealed for a total of 10 minutes after removing the leads from the battery. While I’m waiting, I dip the hot portion of the Varrox in water to immediately cool it and start the same procedure with the next hive. When the 13 minutes is up, I remove the foam, re-open the top entrance and walk away. The first time I did this treatment I only did one hive at a time before moving on. During the 2nd treatment, I used 2 timers so I could continue on while the last hive finished it’s treatment. As I recall, to do the 4 hives took me approximately 45 minutes.

Preliminary Results

There are over 1,000 dead mites on this board. I know. I counted them!

There are over 1,000 dead mites on this board. I know. I counted them!

Hive 1:
Pre-treat inspection: 24 hour mite drop of 10 – 12 on sticky board

1st treatment: 6 Days post-treat with OAV: 1,100+ dead mites on sticky board
2nd treatment: 6 days post-treat with OAV: 1,253 dead mites on sticky board

Hive inspection 6 days after 2nd treatment: Saw the queen who is still laying. Eggs, larvae and brood look good, bees are plentiful, look and act healthy with a few dead bees in hive.

Hive 2:
Pre-treat: 24 hour mite drop of 10 – 12 on stickyboard                    Treated with powdered sugar dusting 2x 1 week apart: mite drop count remaining at 10 – 12/24 hr

6 Days post-treat with OAV: 500+ dead mites on sticky board
2nd treatment: 6 days post-treat with OAV: 728 dead mites on sticky board

Hive inspection 6 days after 2nd treatment: Queen is still laying but was not seen. Eggs, larvae and brood look good, bees are plentiful and look/act healthy, no dead bees in hive.

Hives 3 & 4
Hives were queenless long enough to break brood cycle in August, re-queened late August. Thinking that would nip the mite population I did not do 24 hr mite drop test prior to OAV (my bad…)

Hive 3:
1st treatment: 6 Days post-treat with OAV: about 350 dead mites on sticky board.
2nd treatment: 6 days post-treat with OAV: 296 dead mites on sticky board

Hive inspection 6 days after 2nd treatment: Queen found and is not laying, brood has almost completely hatched, bees plentiful and look/act healthy. I believe she has stopped for winter.

Hive 4:
1st treatment: 6 days post-treat with OAV: About 250 dead mites.
2nd treatment: 6 days post-treat with OAV: 255 dead mites

Queen found and is not laying. Brood almost completely hatched. Bees look/act healthy. Again, I believe she has stopped for winter.


So after 2 treatments I have counted over 4,500 dead mites on sticky boards. I will treat hive 1 and 2 tomorrow but will not treat hive 3 and 4 until I do a final treatment in November when all the hives should be broodless. The reported efficacy of this treatment on broodless hives is approximately 95% mite kill.

Looking in the hives, I would never know these bees were treated. Tho’ they were a bit perturbed when I opened them for inspection, it was cold (55ºF) and at times a bit windy. The eggs, larvae and brood looked normal as did the queen and the rest of the bees. Overall, I’m quite pleased with my choice to use OAV and look forward to seeing how they overwinter.

As to next year, I will absolutely do everything possible to not treat these bees in the fall. I will continue to do my splits, queen capture, mite counts etc. I look at OAV as a backup in case mite counts exponentially rise in late fall. Otherwise, I intend to continue my normal treatment free standard of care. I believe by using OAV this year, I have remained true to my goal of holistic beekeeping. I looked at the entire hive, saw a major mite explosion and treated the hive in the least invasive method possible. Time will tell how successful I am.

I hope your bees are buzzing and that the fall flow has brought you full hives. Go pick some apples and enjoy the rest of autumn!

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