Oxalic Acid sublimation

[AdamD]

Some beekeepers use Oxalic Acid when brood is present to remove varroa mites with multiple applications at 5 day periods. This study from the US says that it is not that effective.

https://academic.oup.com/jinsectscience/article/22/1/15/6523139?login=false

"However, we did not find evidence that frequent periodic application of oxalic during brood-rearing periods is capable of bringing V. destructor populations below treatment thresholds".

[NigelP]

Interesting Adam, thanks for flagging it up.
I used OA vaporization for several years as means of control, but with a sublimox which gives a more efficient vaporization spread as it's active (pressurized) vs passive as the Provap.
Checking mite numbers after 4 treatments suggested that I substantially reduced mite numbers in most hives, but some were very resistant and numbers in these hives remained high even after 7 or 8 vapes, meaning I then had to add Apivar strips to finish them off.
In the end I decided that while expensive, it took far less of my time to add strips to every hive and remove 6-8 weeks later. With over 20 hives vaporization becomes a real chore.
Still vape around any warm period around Xmas as I think OA vaporization works better if the bees are not tightly clustered....this might be wishful thinking on my part

[AdamD]

Its difficult to know why some colonies were so resistant (or rather, the mites in them were). Although you did see a decent mite fall in the remainder of hives which would indicate that the treatment had been effective in those ones.

[AdamD]

It's close to the time of year where a winter oxalic acid treatment is done - I usually do it between Christmas and New Year as it's convenient for me due to work commitments. Some have suggested that it's a bit too late in the year however it must depend on the weather to some extent. (And if you have a polyhive perhaps?).
I have always trickled - it being quick and I have not seen any queen issues as a result.
Am I doing it at the wrong time and the wrong technique? Any thoughts?

[MickBBKA]

I wonder Nigel if what you have found is a result possibly of colonies having continuous brood rearing over winter like many do now. As we know vaping is aimed at phoretic mites so possibly several frames of brood at various stages could be hiding a lot of mites protected from vaping which is only effective for a very short time opposed to strips over 6 weeks.
I use strips in autumn with vapes as req up until spring. I am still not convinced about treatment free keeping. Studies I have read about island based conditions are miles away from what folk are claiming here in the UK. 80% losses are the norm in what I have read.

[Spike]

It's close to the time of year where a winter oxalic acid treatment is done - I usually do it between Christmas and New Year as it's convenient for me due to work commitments. Some have suggested that it's a bit too late in the year however it must depend on the weather to some extent. (And if you have a polyhive perhaps?).
I have always trickled - it being quick and I have not seen any queen issues as a result.
Am I doing it at the wrong time and the wrong technique? Any thoughts?

its often mild at Christmas. Will there be brood? Or do they start in January?

[MickBBKA]

[/quote]
its often mild at Christmas. Will there be brood? Or do they start in January?
[/quote]

Its a case of knowing your bees in your local area, all the old wives stuff still peddled by the BBKA is meaningless these days.
Lots of colonies now don't have a brood break at all in Winter. Most of my bees have a brood break in September/October when the powers that be inform us they are raising the Winter bees. I check mine with a temperature probe. It was 12c here today, it will be colder in May and June where my bees are. I treat all colonies in December and January regardless.

[AdamD]

I looked at one of my colonies in September and I wondered whether they had 'lost' their queen as there was little brood and the brood cells were being "backfilled" with honey. I then checked two more and they were the same. Unless all three colonies miraculously lost their 2023 queens at the same time which is highly unlikely, the girls had decided to have a rest.
I have never really looked at brood frames in December so I don't know the state of the brood and whether the queen is laying at that time of year. (If you can't do anything about what you find, then there's no point in disturbing them). They are sometimes miffed enough that you are cranking the lid off their home during oxalic dribbling treatment (and they are too cold to fly) that I don't want to disturb them any more than necessary.

I only have one glass crown-board so can't look to see what's going on - although with a well-provisioned colony, the bees could be low down in the hive. (And relating to the polyhive thread, bees didn't seem to cluster in winter when I had my Paynes poly - a bit like happily walking around the house in winter with nothing more than a T shirt on.).

[MickBBKA]

Polycarb crown boards are on all my colonies. They are almost all like this at the moment and although I haven't taken any temp readings the crown boards are all very warm to touch and I very much believe they are rearing brood. 2 nucs I have look ready for a full brood and have increased massively since the end of October But they are not getting them ! You can see why I think of poly hives as emperors new clothes

[AdamD]

In my inspection and treatment yesterday, my colonies were clustered and mostly further down the comb. I didn't notice any warmth on the crown-boards.
Many of my wooden crown-boards have porter bee escapes in them which will be gummed up solid at this time of year. Why do you ventillate the top Mick. Do you have insulation above the crown-boards?