Oxalic Acid Treatment

[Gscot]

My first Winter keeping bees and going to treat with Oxalic Acid."Is it just a case of trickling the acid down the frames on top of the bees after slightly heating?"Would be thankful for any advice

[gavin]

The slightly heating isn't so important - maybe lukewarm is kinder than freezing - but yes, trickle the requisite amount right on the bees where you find them between the top bars of the frames. I'll be doing mine next month.

[Jimbo]

Hi Gscot,

I make a 3.2% Oxalic acid in a weak sugar syrup solu. When you make up the solution you don't want to leave it too long before using it as it can deteriorate.
I trickle 5ml down each seam of bees using a syringe. If you have a strong hive you need about 50ml per hive. If the hive is weaker hive you may only need 20 - 30 mls i.e. 5ml where you see bees between the frame. When you trickle do it slowly so the Oxalic does not run straight through the hive. When weighing out the Oxalic powder wear a face mask and gloves as Oxalic powder is bad for if you ingest it or inhale the dust. It may also cause burns and dermatitis if in long contact with the skin.

[Jon]

The basic mix is 7.5g Oxalic powder, 100g water and 100g sugar which gives enough for 4 or 5 colonies.
If you stick with this ratio you can't go far wrong.
last year I multiplied by three and used 22.5g Oxalic, 300 sugar 300 water which gave me just over 500ml. I had enough for 12 colonies and still had to throw away about 100ml.
I brought the mix to my apiary in a half litre coke bottle and used an applicator which I got from Thorne for a couple of quid. You fill it and it measures out 5ml when you tip it. It fills a bit like a bar optic.
It was around freezing point the day I treated in December so I stood the bottle of Oxalic solution in a plastic container which I topped up every 10 minutes with hot water from a flask.

It only costs a few pence per colony to treat like this.
If you work quickly you shouldn't have the crown board off for more than a couple of minutes.

[Calum]

Hi Jon
your post is very interesting. How much do you give each colony (large- mediun- small)?
This would be very important depending on the strenght I think?
Here we get the acid solution and just have to add the sugar...

[Jon]

5ml per seam of bees so it varies according to colony strength.
My strongest would have 8 seams in a winter cluster so 40 ml.
Some of the nucs would get no more than 15ml.

I bought 500g from Thorne for about a fiver a couple of years ago.

The box says:

Preparation: Mix 1litre of water with 1k sugar using a clean container in a secure area. Add 75g oxalic acid dihydrate (which contains 71.4% oxalic acid) Mix thoroughly. The resulting solution will provide 3.2% oxalic acid. This should be enough to treat 25 hives.

You can buy pre mixed oxalic from Thorne as well but it won't keep. If you have the powder it should last for ever. 30g should treat all my colonies and nucs this year.

[Rosie]

My theory is that the 5ml per seam rule was developed on the continent with bigger hives than those that most of us keep. I use 2.5ml in my National frames and less towards the edge of the nest where the bees only partially fill the frame. It is unusual for me to use more than 12 ml per colony.

If I kept Buckfasts it might be a different story.

I don't want to influence others to copy me but I have about 100 hive winters of experience with this dose rate and am quite happy with it.

Steve

[Jon]

Rosie:
What sort of mite numbers have you seen after oxalic and how many seams of bees has your average colony?
Do you see a couple of dozen or hundreds?
Mine tend to overwinter with small clusters and 5 seams would not be unusual in December.
I used oxalic for the first time last year and didn't have time to check the mite count as I was abroad for 7 weeks shortly after treatment.
With the 5 ml per seam you are supposed to start at the edge of the frame and apply right to the other edge so if the bees do not reach to the edge of the box some of the oxalic must fall straight to the floor. In that sense it part regulates the dose and a small seam of bees does not get the full 5 ml.

PS Jimbo, I would be curious to see your replies to the above questions if you have used oxalic over 8 years.

[Jimbo]

Hi Rosie,

I think it was the Swiss who did a lot of work on Oxalic acid. If I remember it is the concentration that is important. If you keep it about 3% it will have little effect on the bees If you use higher concentrations than this you start to run into problems. I should also have mentioned in an earlier post you can only dose with the Oxalic trickle method once a year. If you you use it too often you again run into problems as I think the bees ingest it.
I have been using the Oxalic acid trickle method for more than 8 years and have not noticed any adverse effects

[Rosie]

I have been using the Oxalic acid trickle method for more than 8 years and have not noticed any adverse effects

Neither have I but I have used it for about 6 years. Some people advocate using it on a swarm while they are still broodless but I don't because it would prevent me from using it during the winter. I too believe that one dose per year is sufficient but I do worry about its effect on the queen if she lives long enough to experience a number of doses. Hopefully she would not ingest it. Some people justify 2 doses a year because the bees that suffered the first dose would be dead by the time the second dose is administered. Only the queen would see multiple doses unless it was done more than once during the winter.
Jon, I don't measure mite drop on all my colonies, in fact I only have 2 varroa floors but I do put them under a couple of hives during the treatment. I used to get drops of up to 1200 mites but these days I don't see enough to be worth counting. I would guess less than 50. I do, however, give them a half-hearted dose of thymol crystals before the winter to try to strengthen the winter bees. I don't get much of a drop then either though.

I sometimes wonder if something is working on the mites that is outside our control and is doing the work for us. After all there are lots of potential pathogens in our environment that is exotic to the mites so it would not be surprising if one if them was getting the better of them. Nature might be giving them their comeuppance


Steve