How many OAV treatments in winter can they tolerate?
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  1. #1
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    Default How many OAV treatments in winter can they tolerate?

    Curious as to how many OAV treatments bees can tolerate before dying in the winter.

    I've treated once in the late fall, but I've read that some beekeepers treat AGAIN in December, if there's a warm day.

    Will multiple winter treatments kill hives?

    So far, I didn't notice any dead bees from the November OAV treatment, but I don't want to test my luck...

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  3. #2
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    Default Re: How many OAV treatments in winter can they tolerate?

    OAV doesn’t kill hives, Queens, brood, workers, whatever.
    To be effective in Winter it should be around or above 6C, (45F?) so the bees aren’t tightly clustered.
    My Varrox manual says to not use below +4C.
    Lots of OAV threads here, check them out.
    I treated my hives with OAV every 5 days from late August to early October, no issues.
    Brian
    53N 115W

  4. #3
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    Default Re: How many OAV treatments in winter can they tolerate?

    Quote Originally Posted by BDT123 View Post
    OAV doesn’t kill hives, Queens, brood, workers, whatever.
    To be effective in Winter it should be around or above 6C, (45F?) so the bees aren’t tightly clustered.
    My Varrox manual says to not use below +4C.
    Lots of OAV threads here, check them out.
    I treated my hives with OAV every 5 days from late August to early October, no issues.
    Brian
    53N 115W
    I'm not asking about October treatments, I'm asking about November, December/ January treatments in very cold climates where snow accumulates and doesn't go away.

    Whether or not hives in those climates will die if one OAV during the winter more than one time, or repeatedly.

    Thanks.

  5. #4
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    Rutland County, Vermont,USA
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    Default Re: How many OAV treatments in winter can they tolerate?

    As has been stated by BDT123, OAV at any time of the year will not kill your hive. However, if you only treated once in November and did not use any other treatments before that, your hive may die from mite related diseases. OAV will not penetrate the cappings so if your hive had brood in November (and I assume it did) then there were a lot of mites that were not killed. That is why OAV is done in a series of treatments. If your hive has no brood, like in late December for me, then a "one shot" is commonly done to kill whatever mites are still present on the bees (phoretic). The fact that there is snow and its cold does not matter. The treatment is more effective if the bees are not tightly clustered. That's why its preferred to do it on a "warmish" day around 40-45. J

  6. #5
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    Default Re: How many OAV treatments in winter can they tolerate?

    Quote Originally Posted by Fivej View Post
    If your hive has no brood, like in late December for me, then a "one shot" is commonly done to kill whatever mites are still present on the bees (phoretic).
    I agree. VOA in winter is pretty-much like sprinkling flea-powder over your dog - it's not going to matter much whether you use one packet of powder or half-a-dozen - the excess is just a waste of time and materials - the dog won't care.

    I did read a paper where the author recommended a second follow-up treatment a few days later - I can't remember his reasons - I'll try and find that paper but I'm a bit pushed for time right now. But imo, trying to kill every last mite, whilst an understandable objective, it fairly pointless whilst there are still mites 'out there' just waiting to re-infest treated colonies. So for me, during Winter a single treatment is all they get.
    LJ
    A Heretics Guide to Beekeeping http://heretics-guide.atwebpages.com/

  7. #6
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    Default Re: How many OAV treatments in winter can they tolerate?

    If the colony is broodless for the winter treatment and the treatment is effective (and you should expect 90+%) then there seems little point in repeated treatments in the winter. Of course, if they're not broodless then you have to contend with more mites emerging from capped cells after the OA has 'worn off'. In that case repeated treatments are justified. There will be no drifting/robbing in winter so whatever is in the hive is what you have to treat, and the very best way to get them is when there is no brood in the colony.

    As repeatedly stated here and elsewhere, colonies can tolerate repeated treatments with vaporised OA ... but, if you time it right in the winter, you shouldn't need to.
    The Apiarist - beekeeping in Fife, Scotland

  8. #7
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    Default Re: How many OAV treatments in winter can they tolerate?

    Quote Originally Posted by fatshark View Post
    If the colony is broodless for the winter treatment and the treatment is effective (and you should expect 90+%) then there seems little point in repeated treatments in the winter. Of course, if they're not broodless then you have to contend with more mites emerging from capped cells after the OA has 'worn off'. In that case repeated treatments are justified. There will be no drifting/robbing in winter so whatever is in the hive is what you have to treat, and the very best way to get them is when there is no brood in the colony.

    As repeatedly stated here and elsewhere, colonies can tolerate repeated treatments with vaporised OA ... but, if you time it right in the winter, you shouldn't need to.
    Am I guaranteed not to kill hives if I treat with OAV twice or more when there's snow on the ground?

  9. #8
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    Default Re: How many OAV treatments in winter can they tolerate?

    Quote Originally Posted by username00101 View Post
    Am I guaranteed not to kill hives if I treat with OAV twice or more when there's snow on the ground?
    I don't know if anyone can guarantee that, but I've never heard of bees getting killed by OAV unless they were burned.
    I'm in Northern VA, and treat several times through the winter with one-shot OAV. I don't have hard and fast timelines, but generally hit them every six weeks or so on a day when they're flying at least a little. Around Thanksgiving, around New Years, sometime in Feb or early March.

  10. #9
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    Default Re: How many OAV treatments in winter can they tolerate?

    Hasan Al Toufailia, Luciano Scandian, Kyle Shackleton & Francis L. W. Ratnieks (2018) Towards integrated control of varroa: 4) varroa mortality from treating broodless winter colonies twice with oxalic acid via sublimation, Journal of Apicultural Research, 57:3, 438-443, DOI: 10.1080/00218839.2018.1454035
    https://www.tandfonline.com/doi/abs/...nalCode=tjar20
    In winter 20142015, we treated 22 broodless honey bee colonies with 2.25 g oxalic acid (OA) via sublimation on 23 December 2014 and again on 6 January 2015. Varroa numbers were determined before and after OA application by extracting mites from samples of workers. Mean varroa mortality from both applications combined was 99.6%, which is greater than the 97.6% mortality from a single treatment shown by our previous research. We determined whether double OA application was more harmful than single application, by comparing 12 colonies that had been double treated with 12 single-treated colonies. There was no difference in colony performance on 5 May 2015 (100% survival in both groups; 5.5 frames of brood in single-treated colonies vs. 5.3 in double-treated colonies). Varroa mortality from the first application, 96.8%, was significantly higher, p < 0.001, than from the second 87.2%. Ten of the 22 study colonies were killed 14 days after the second OA application to precisely quantify varroa levels. The mean number surviving was 6 (range 218). Worker numbers averaged 5,644 bees (range 3,3528,692). To confirm the results a small second trial was made the following winter with 10 colonies. Results were similar. Again, combined varroa mortality was very high, 99.4%, with greater mortality from the first, 98.3%, than the second, 64.1%, application. Overall, the results indicate that double application of OA is worthwhile to beekeepers in varroa management. It is not harmful to colonies and by killing c. 99.5% of the varroa it reduces varroa populations to such an extent that 78 doublings, which would take more than one year, are needed to build back to the original level.

  11. #10
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    Default Re: How many OAV treatments in winter can they tolerate?

    Quote Originally Posted by little_john View Post
    I did read a paper where the author recommended a second follow-up treatment a few days later - I can't remember his reasons - I'll try and find that paper but I'm a bit pushed for time right now.
    ... combined varroa mortality was very high, 99.4%, with greater mortality from the first, 98.3%, than the second, 64.1%, application. Overall, the results indicate that double application of OA is worthwhile to beekeepers in varroa management.
    That's the one - thanks
    LJ
    A Heretics Guide to Beekeeping http://heretics-guide.atwebpages.com/

  12. #11
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    Default Re: How many OAV treatments in winter can they tolerate?

    Quote Originally Posted by msl View Post
    Hasan Al Toufailia, Luciano Scandian, Kyle Shackleton & Francis L. W. Ratnieks (2018) Towards integrated control of varroa: 4) varroa mortality from treating broodless winter colonies twice with oxalic acid via sublimation, Journal of Apicultural Research, 57:3, 438-443, DOI: 10.1080/00218839.2018.1454035
    https://www.tandfonline.com/doi/abs/...nalCode=tjar20
    Looks like there WAS a negative effect of multiple treatments, a 4% decline in brood. That's only for 2 treatments.

    For more, say 5 treatments, in the fall and winter - could be as high as 20% less brood.

    This study didn't detail if any previous treatments were applied.

    Does anyone here have access to these full articles, I'd like to read more than the abstract.
    Last edited by username00101; 12-03-2019 at 02:20 PM.

  13. #12
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    Default Re: How many OAV treatments in winter can they tolerate?

    User, just go with what needs to occur.
    Are you still concerned with mite levels?
    If you are, treat at appropriate temperatures. No harm, no foul.
    If mite counts are low, don’t treat.
    Your call, but you can’t kill your bees with appropriate use of OAV. Cluster spread is important for efficacy.
    Brian

  14. #13
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    Default Re: How many OAV treatments in winter can they tolerate?

    Username, just treat the darn bees now if you haven't already, and again at the end of the month. I did this regimen last year, had 100% survival rates, and had a zero mite count in March when the state inspected my hives. Hard to beat those kinds of numbers, no matter what you read elsewhere.
    Thankfully, the bees are smarter than I am. They are doing well, in spite of my efforts to help them.

  15. #14
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    Default Re: How many OAV treatments in winter can they tolerate?

    I am with JW.
    Your 4% reduction in brood is not correct without knowing what the variability was hive to hive. The researchers did the statistics and stated there was no difference. Statistically significant is not the same as the averages were not equal.

  16. #15
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    Default Re: How many OAV treatments in winter can they tolerate?

    Thanks for posting "msl", that's the source of my 2X, 14 days apart winter OAV. It works as I did not have to treat again until the fall Varroa invasion arrived.

  17. #16
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    Default Re: How many OAV treatments in winter can they tolerate?

    Just got back from Australia and New Zealand, did an OAV prior to leaving on the 10th of November but am sure that there was still some brood in some hives so plan to do another treatment in December temperatures permitting and might even do a third treatment if I see much varoa fall and feel quite comfortable that this will do my colonies more good than harm.

  18. #17
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    Default Re: How many OAV treatments in winter can they tolerate?

    When I do OAV in non-flying weather (so, below 45, and cloudy, or below 40 and sunny), I can hear a "roar" during the treatment, and for about 20 min after. Then they behave like a non-bothered winter hive. I also don't see more dead bees chucked out after.

    Sometimes during treatment a few bees try to come out, sometimes they don't. When I have had a hive die over the winter, the bees had oodles of mites on them. The hives that got treated with OAV effectively don't die.

    I look at how many mites drop on the removable board to decide when I am done. If in Dec the mite drop is 50 or less, then I'm done. OAV is in fact a monitoring tool, in a clunky sort of way.

  19. #18
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    Default Re: How many OAV treatments in winter can they tolerate?

    We hit them twice in winter. Even if the OAV does stress them a bit nothing stresses a hive like varroa.
    Splitting a first year hive successfully https://youtu.be/ZfRTreQ-S9c

  20. #19
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    Default Re: How many OAV treatments in winter can they tolerate?

    FYI trishbookworm: I got a fairly good plot of Fall Varroa affects by counting dead Varroa on a sticky board. Connecting the individual hive plots with hive history made sense. Fall Varroa migration timing was clearly connected with end of flow and robbing by summing dead Varroa for all nine hives and plotting against time.

    An obvious Varroa resistant hive showed up as well as one that is not or had another event intermingled. The results seemed "clunky" until I sorted the results into a graph to get a coherent story. In my area, southern RI, the Varroa invasion started about 9-26-09, peaked on 10-13-19 and dropped dramatically by 10-18 -19. One hive continued with high numbers, above 450, for two more weeks before dropping sharply; cause unknown.

    It seemed to be a long Varroa Invasion Season this year. I treated 10 times, 8 as treatments and 2 as test treatments to verify status. I also had one hive put through an intentional brood break and treated on 9-26-19. Post break treatement on 10-3-19 clearly showed the invasion as the hive had ample foragers and active laying going on post brood break. My Varroa problems seems to be related to my neighbors' hives.

  21. #20
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    Default Re: How many OAV treatments in winter can they tolerate?

    The hard part is finding a day over 45 degrees when you are not working. The one treatment (OAV) in December works fine for me. Of course treated in aug/ sept too.

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