top of page

Winter Oxalic Acid Sublimation to control Varroa destructor

During the Winter months I spend a few precious hours out with the bees treating them with oxalic acid to try to remove as many phoretic Varroa destructor mites as possible. These mites are quietly sitting on the backs of our bees and not buried within the cells of developing larvae, thus we are able to kill them using the oxalic acid vapour treatment.

Varroa hide in sealed cells where Oxalic Acid can't normally penetrate

In years gone by, I've normally used Oxalic Acid to treat my bees using the trickle method, this is where the Oxalic Acid is dissolved in light sugar syrup and simply trickled over the seams of honeybees in the cluster. The syrup mingles with the bees and the varroa get a coating and die.

Following discussions with fellow bee farmers and reading several research papers on the use of Oxalic Acid treatments I decided to switch to the sublimation method, as it appears to be more effective at killing the Varroa mites and less harmful to the bees than other methods.

Further investigation showed that there were several units out there that would be up to the job for the number of colonies I was looking to treat. I have around 70 colonies currently that need managing for Varroa and the smaller, single use, wand type units just weren't going to be man enough for the job. The ProVap220 was being advertised in the USA but I couldn't find anyone selling it in the UK and this was just the right unit for me. Not being able to easily get hold of one wasn't going to stop me, so after much investigation I managed to get in touch with the manufacturer who offered me the sole UK distribution rights for the unit, hence we now sell them on our website here.

I mentioned the research papers that I had read and one in particular contained some excellent details about the amount of Oxalic Acid Dihydrate that needed to be used to maximise the efficacy whilst keeping the honeybee mortality to a low level.

If you'd like to check out the scientific paper that I refer to, you can find details in the link below but the author and title details are:

Hasan Al Toufailia, Luciano Scandian & Francis L W Ratnieks (2015) Towards integrated control of varroa: 2)comparing application methods and doses of oxalic acid on the mortality of phoretic Varroa destructor mites and their honey bee hosts, Journal of Apicultural Research, 54:2, 108-120, DOI: 10.1080/00218839.2015.1106777

Anyway, if you decide to go down the route of Oxalic Acid sublimation rather than the trickle method you really must take your personal safety and that of anyone helping you, very seriously. Oxalic Acid when vapourised is a very harmful substance, potentially causing all manner of problems for anyone breathing it in or getting it in their eyes.

The ProVap220 with OA Bowls, and importantly, goggles and face mask rated for organic acids

You must use the correct Personal Protective Equipment, at the very least use a proper face mask (not a simple dust mask), one that is rated for organic acids, along with eye protection that will keep the vapour completely away from your eyes, and don't go thinking wearing reading glasses is going to be enough!

Protected with Face Mask and Goggles

The ProVap220 comes complete with measuring spoon and two OA bowls. I use 2.25g of Oxalic Acid Dihydrate crystals for each hive which is placed in the white ceramic bowl. The bowl has an "O" ring to create a seal when it is pushed onto the receiving bowl of the heated dish of the unit itself.

The ProVap220 is held upside down over the ceramic bowl and pushed down to secure the bowl in place. For this part of the operation you need a decent heat resistant glove or you will burn your hand!

It's important to get the nozzle in place before you turn the unit back upright otherwise you will get an immediate release of vapour from the nozzle and it will go anywhere except into the hive!

The treatment takes about 20-30 seconds to complete and while the ProVap220 does it thing, you can get the second bowl ready for the next hive.

Back view of the hive with varroa floor insert, foam block and golf tee in place

Preparing the hive is straightforward, block the entrance with foam or a cloth, remember to put in the varroa floor and also block any gaps with foam at the back to prevent vapour from escaping. I have a small hole drilled into the back of the floor where the nozzle fits and is plugged with a wooden golf tee when not in use. You can simply insert the nozzle at the front entrance using a cloth but it will melt foam if you have used this to block the entrance.

The heat will damage poly hives, so make sure you use an eke.

I also use Happy Valley Honey Poly Langstroth hives and Maisemore Commercial Poly Hives, of course you're going to melt the poly material if you put the heated nozzle against it, so during the latter part of the Autumn I fitted wooden eke's to the hives to enable me to treat them without damaging the hive body material.

I created a YouTube video of the entire process which is currently available to my Patreon subscribers here. If you're not a subscriber you can join for just $1 per month to access all of my video content or wait a while for the video to become available on YouTube.

The results of our Winter treatments can be checked after a few days when we take a look at the varroa boards to see if we have any mite drop. Undoubtedly, any help we can give the bees now will prove invaluable in the Spring when the colonies are looking for a fast start, unhindered by Varroa destructor.

Please do get in touch if you have any questions and check out my Patreon page if you would like to support me in producing lots more content for beekeepers around the world.


2,786 views0 comments

Recent Posts

See All


bottom of page