# Spring OAV treatment in NorCal?



## snl (Nov 20, 2009)

OAV will only kill phoretic mites (those on the bees) thus limiting the mite kill as most are in the brood. That said, it would do no harm to either the brood, bees or queen. Look to your drone brood, if you find mites, I'd treat at least once prior to placing supers.

I believe that killing mites prior to placing the supers potentially limits the mite growth numbers in the future......

Again, your kill is limited to phoretic mites..


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## Axtmann (Dec 29, 2002)

Believe it or not, you should not give an advice using OAV in spring. It's not a good idea, except if you are selling the vaporizer. The beginners think every is OK after the treatment, but most of the time, it is not. 

Beginner
Think about, if 95% of the mites hiding in closed cells, how long will it take and your hive is gone? If you have a mite problem in spring, you made a mistake last fall. Use a treatment that is recommended for the warmer temperatures and works even when bees have brood, like formic acid pads or thymol strips. Even cutting the drone brood during the year will reduce the mites not more than 50%, if you're lucky. 
There is always somebody with a different opinion, but this are my experiences.


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## snl (Nov 20, 2009)

Axtmann said:


> Believe it or not, you should not give an advice using OAV in spring.


I believe I qualified my answer as the poster asked about using OAV in the spring. You are correct in that there are other and better alternatives. However, an intensive treatment of OAV for a heavy mite load is not unreasonable for those who use nothing else. Four treatments, 5 days apart will kill a lot of emerging mites prior to them entering a cell about to be capped to start their reproductive cycle.


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## enjambres (Jun 30, 2013)

I, for one, hope that the promised approval of OA use comes with scientifically-based instructions for best-practices treatment regimens!

I don't think that "95%" of a colony's mites are protected under the cappings from OA exposure. The math doesn't work out on that. But a large portion, perhaps even more than half, of them certainly are. 

But I also note that the folk-wisdom connected to OAV has morphed from (last year) three treatments spaced 5 days apart to (at present) _four_ treatments. Where will it end?

I like and use OAV in my hives; it seems to be working and I believe others have used successfuly for longer than I have.

But any miticide, if used too frequently, or conversely, used in ways that are sub-therapeutic, will eventually become ineffective and will be lost to us as a critical weapon. Let's not hasten that day!

To the OP: you may find the information you need on Randy Oliver's site: Scientific Beekeeping. He has written a good deal about his experience using OA, and in California, too. 
Enj.


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## Lburou (May 13, 2012)

SNL, I've read reports that the percentage of phoretic mites is 8%, also read it can be as high as 80%. What is the best estimate of mite numbers in the brood as opposed to hitchhiking on the bees? Are there reliable estimates of phoretic mites for each month of the year (realizing the number of phoretic mites skyrockets as brood nest shrinks and disappears over winter)?


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## Beregondo (Jun 21, 2011)

I'd recommend reading the following articles, and make your own (informed) decision:

From Scientific Bekeeping ( http://scientificbeekeeping.com/varroa-management/treatments-for-varroa/ ):

 
The Learning Curve – Part 1: 2009 Progress Report 

The Learning Curve – Part 2: Killing Mites without Killing Your Bees

Oxalic Acid: Questions, Answers, and More Questions: Part 1 of 2 Parts 

Oxalic Acid: Heat Vaporization and Other Methods: Part 2 of 2 Parts 

Oxalic Acid Treatment Table

From the current (January 2015) issue of _*American Bee Journal*_, page 83:
_*"Messin' with Varroa 2014"*_


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## snl (Nov 20, 2009)

Lburou said:


> SNL, I've read reports that the percentage of phoretic mites is 8%, also read it can be as high as 80%. What is the best estimate of mite numbers in the brood as opposed to hitchhiking on the bees? Are there reliable estimates of phoretic mites for each month of the year (realizing the number of phoretic mites skyrockets as brood nest shrinks and disappears over winter)?


I've not seen any studies on your question. However, as you've stated...."the number of phoretic mites skyrockets as the brood nest shrinks," which in part answers your question as to the mite percentages in the brood as opposed to phoretic mites. The mites are eager to mate (almost as soon as they emerge) and will readily climb back into a cell that's about to be capped. That's why with a late summer/early fall/early winter treatment when the brood-nest is contracting (and there are no cells to climb into) treatment is so effective.
In spring, with the brood nest expanding you’ll see a lot less phoretic mites. Your mite counts could be deceiving (you thinking they are low) when in fact most of the mites are in brood. That’s why I no longer look to phoretic mite counts, I look in drone brood. I believe drone brood is the true indicator of mites as mites will readily migrate to drone brood.
I don’t believe OAV is the best treatment for high mite counts in the spring. There are better. You would have to do it too often to catch the mites as they are exiting with the emerging bees. HOWEVER if you insisted on doing so (and there is no reason you could not,) and time allows, I would do it 4 times (as opposed to 3 in the fall,) five days apart to vaporize as many mites as possible prior to placing the supers. 

I’ve use OAV several times in the spring and again, while it is time consuming, from the looks of sticky board; it does knock the mites down. I've not lost a hive to mites since I started treating exclusively with OAV.


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## Eddie Honey (May 30, 2011)

Will the OAV kill the mites that have jumped into a cell and the cell is in the process of being capped?


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## snl (Nov 20, 2009)

Eddie Honey said:


> Will the OAV kill the mites that have jumped into a cell and the cell is in the process of being capped?


If the oxalic acid comes in contact with the mite, yes...... OA must contact the mite in order to destroy it. While the exact method of OA destroying the mite is hazy at best, it is believed that it destroys mouth parts and the feet as it enters into the cuticle...


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## Lburou (May 13, 2012)

snl said:


> If the oxalic acid comes in contact with the mite, yes...... OA must contact the mite in order to destroy it. While the exact method of OA destroying the mite is hazy at best, it is believed that it destroys mouth parts and the feet as it enters into the cuticle...


I found these pictures somewhere....Ostensibly showing before and after oxalic acid exposure. The proboscis would be the mouth part. HTH


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## bison (Apr 27, 2011)

Thanks for the comments... but I'm still not sure if a spring treatment to knock down any mite load is a good idea or not. I understand that OAV doesn't get to the mites in capped cells, but if indeed the treatment doesn't hurt the bees it seems as though a preventative treatment or two in spring wouldn't hurt.


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## Lburou (May 13, 2012)

bison said:


> Thanks for the comments... but I'm still not sure if a spring treatment to knock down any mite load is a good idea or not. I understand that OAV doesn't get to the mites in capped cells, but if indeed the treatment doesn't hurt the bees it seems as though a preventative treatment or two in spring wouldn't hurt.


Randy Oliver seems to recommend OA during the winter or late fall when the brood nest is empty, and rotating other treatments the remainder of the year. He has a chart of the beekeeping year and a recommended rotation of various treatments. That chart is probably in one of the scientific beekeeping links above. HTH


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## knute (Mar 10, 2013)

According to what I've read and also heard from Randy Oliver, approximately 2/3 of the mites in the hive are under the cappings, so OAV treatment during spring is not as effective as it would be during a period with less brood.

But, OAV can be very effective if used with the right timing with a walk away split. Queen with no brood and plenty of nurse bees and drawn comb in one half, and all the brood (and nurse bees to cover) in the other half. This results in a brief period in both hives with no capped brood, and thus no mites hiding under the brood cappings- perfect conditions for OAV treatment. If the queenless side doesn't successfully re queen, you can recombine (or add a mated queen), so the relative risk is low.


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## BernhardHeuvel (Mar 13, 2013)

1. Oxalic acid has a half life of two weeks, so it stays at least a month in the hive.
2. Oxalic acid does accumulate in open nectar cells and is preserved within the nectar and honey (or winter food) for years. So there is a good chance you contaminate your honey if you treat in Spring with oxalic acid. (This is why it isn't allowed for use in Spring in Germany.)

Better cut some drone brood or do a split. You may get only 30 mites out by cutting drone brood, but that can make a difference. See chart below showing the difference if a colony starts with 30 mites, 100 or 300 mites into the season. The reproduction rate is the same in all cases: 1.6 by every broodcycle.


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## knute (Mar 10, 2013)

BernhardHeuvel said:


> 1. Oxalic acid has a half life of two weeks, so it stays at least a month in the hive.
> 2. Oxalic acid does accumulate in open nectar cells and is preserved within the nectar and honey (or winter food) for years. So there is a good chance you contaminate your honey if you treat in Spring with oxalic acid. (This is why it isn't allowed for use in Spring in Germany.)


Bernard, I'd love to see the data behind these assertions- none of the studies I've seen support that position that the oxalic acid lingers in the hive. I have seen a study that measured the rate at which the bees metabolized oxalic acid that was ingested following trickle treatment, and that's consistent with a "2 week half life", but that doesn't correlate with oxalic acid levels in the nectar or honey. Here's a link to a Danish study from 1998 that treated hives at the end of March (spring) with oxalic acid, and measured the oxalic acid levels before treatment, 8 days after treatment, and again in the honey harvested in June, and the control hives (no oxalic treatment) actually ended up with higher levels of oxalic in the honey than the treated ones. This suggests no evidence of residue buildup...

See: http://www.beekeeping.com/articles/us/spring_treatment_oxalic_acid.htm


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## shinbone (Jul 5, 2011)

enjambres said:


> But any miticide, if used too frequently, or conversely, used in ways that are sub-therapeutic, will eventually become ineffective and will be lost to us as a critical weapon.


Is that really true specifically for OA? How could the mites adapt to having their mouth parts burned off? Put another way, how could bison ever adapt to being driven off a cliff?



Also, in regards to the Heilyser Technology photo, I would love to know more about how the series of photos was made because it is the exact same mite in the exact same orientation in both photos. Accordingly, it appears that a mite was somehow fixed in place, photographed with a scanning electron microscope, somehow exposed to some form of OA , then photographed again without moving the SCM, or . . . ? At the very least, it is not before and after photos of mites from a hive. (Not saying the photos are faked, etc., just wondering how they were made to better interpret them).





.


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## Swampsquash (Oct 25, 2014)

shinbone said:


> Is that really true specifically for OA? How could the mites adapt to having their mouth parts burned off? Put another way, how could bison ever adapt to being driven off a cliff?
> 
> 
> 
> ...


Yeah this is what I was wondering myself!


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## knute (Mar 10, 2013)

So, no studies or references to show that oxalic acid actually builds up in the hive? The best reason not to use OAV (or trickle) in spring is because it isn't very effective because of all the capped brood, not because it builds up in the hive or affects the honey in any meaningful way.

If there is any study that shows oxalic buildup resulting from treatment, I am very interested to see it.



BernhardHeuvel said:


> 1. Oxalic acid has a half life of two weeks, so it stays at least a month in the hive.
> 2. Oxalic acid does accumulate in open nectar cells and is preserved within the nectar and honey (or winter food) for years. So there is a good chance you contaminate your honey if you treat in Spring with oxalic acid. (This is why it isn't allowed for use in Spring in Germany.)
> 
> Better cut some drone brood or do a split. You may get only 30 mites out by cutting drone brood, but that can make a difference. See chart below showing the difference if a colony starts with 30 mites, 100 or 300 mites into the season. The reproduction rate is the same in all cases: 1.6 by every broodcycle.


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## BernhardHeuvel (Mar 13, 2013)

knute said:


> So, no studies or references to show that oxalic acid actually builds up in the hive?


In Spring. That's only valid for spring treatments, simply there has no work been done on it. There is only one German study, that looks at buildup when using it continuously from April through July. Every three weeks. They of course found a higher oxalic acid in the honey. But not in hazardous amounts or even above the natural range of oxalic acid. 

Another interesting find of this study was, that it didn't influence the mite population at all. So in autumn, the hives had the same mite population as in the untreated control group. There was a significant mite drop after each treatment. But the mites seemed to be able to recover from those losses. (Presumbly by accelerating reproduction.)



knute said:


> The best reason not to use OAV (or trickle) in spring is because it isn't very effective because of all the capped brood, not because it builds up in the hive or affects the honey in any meaningful way.


I don't know. There is a written law and an unwritten ethic in our country, that honey should be as pure as is possible. So treatments are not allowed after the first day of the current year until the last harvest. So by January the 1st, 2015 all treatments (with miticides) have to be finished. Until the last honey harvest. Period. It should be common sense that a treatment before a harvest plus a half life of two weeks leads to accumulation. To avoid it, don't do it.

If you have done your homework last summer and winter, you shouldn't need to treat in early Spring. That is probably why very few studies look into spring treatments and residues from them. The urgency to treat in Spring may differ in a different climate (warm winters in the South), of course.

Beside the residue buildup, there is another reason why oxalic acid shouldn't be used all year round: resistance. There is a good chance that the surviving mite do get resistant to all the acids (formic, oxalic,...) if you use the acids too often. In Berlin there is a researcher who has found hints, that mites evolve a certain resistance to acids. (By a harder shell, more wax on the shell and other mechanisms. Nature is inventive...) A lot of beekeepers in Germany switch to formic acid with a higher concentration "because it is more effective". (85 % instead of 60 % formic acid.)

So bottom line (for me) is, do avoid Spring treatments, try to solve the problem before winter.


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## snl (Nov 20, 2009)

knute said:


> The best reason not to use OAV (or trickle) in spring is because it isn't very effective because of all the capped brood, not because it builds up in the hive or affects the honey in any meaningful way.


From everything I've read this is true. Remember tho, you are NOT treating with the supers on, so there is no buildup whatsoever in the extracted honey. With all the capped brood (where most of the mites reside) you would have to treat and treat and treat to get the mites as they are emerging with the new bees. You can do it, just a pain and there are better treatments. As was said, the best treatment with OAV is in the fall/early wither.


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## knute (Mar 10, 2013)

Bernard- thanks for the reply. I share your interest in keeping the honey as pure as possible, but the engineer in me wants to quantify question of the actual "build up of oxalic residue"- I'll keep looking for studies on the issue and/or figure out a cost effective way to accurately measure oxalic acid in ppm and commission my own study. I think one reason more studies haven't been done is that the few that have been consistently show that the levels of oxalic acid following treatment don't rise far enough to be outside the range measured in natural, untreated hives; there's no smoking gun to imply urgency for more studies. As well, the flavor threshold will be met long before the oxalic levels would be a health issue. Oxalic acid in rhubarb or oxalis has a very distinctive sour taste...

Regards,

-Knute


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## vdotmatrix (Apr 5, 2014)

What is the incidence of the OAV killing exposed larvae? This would probably bee another reason not to use OAV in the springtime?


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## ABruce (Dec 27, 2013)

For what its worth, I treated my 7, 10 frame double deeps three times at seven day intervals starting last September 1. I still had lots of open and capped larvae. I had no evidence of any die off. Brood production tapered down to almost nil by November 11, which was the start of below freezing temps and I quit checking. So I saw no evidence of damage from the OAV.


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## JTGaraas (Jun 7, 2014)

Should an oxalic acid spray become standard practice at time of "package hiving"?

There is no brood, and the EPA has recognized that almost every package has varroa mites. They have sanctioned the spray to packages, and it makes sense to start without mites if possible. I have been surprised not to see this concept not being promoted in view of the obvious timing advantage - zero brood; no hiding places for the mite!


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## snl (Nov 20, 2009)

JTGaraas said:


> Should an oxalic acid spray become standard practice at time of "package hiving"?


Yes, either that or treatment by the purchaser upon receipt with a spray or vaporization.


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## shinbone (Jul 5, 2011)

vdotmatrix said:


> What is the incidence of the OAV killing exposed larvae?


When properly used, OAV does not harm brood or adult bees.


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## snl (Nov 20, 2009)

shinbone said:


> When properly used, OAV does not harm brood or adult bees.


Or the queen and it does NOT contaminate the comb!


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## Eddie Honey (May 30, 2011)

Research has shown that NOT treating with OAV in the Spring will kill 0 mites


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## Axtmann (Dec 29, 2002)

snl said:


> Yes, either that or treatment by the purchaser upon receipt with a spray or vaporization.


Spraying bees with OA is the best way to kill them self and not the mites. The spray will hit the combs or the bees and rebound, the fine drops are everywhere in the air. Don't use this way, trickle the acid and stay healthy.


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## mbc (Mar 22, 2014)

snl said:


> The mites are eager to mate (almost as soon as they emerge) and will readily climb back into a cell that's about to be capped.


Link?
I'd read that an average of four days were spent phoretic after emerging before diving back in to some, about to be capped, brood- I'll try and remember where I read it and post a link. 
This part of the lifecycle has important implications for treatment regimes and we should try and be as precise as possible about it imho.


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## Brad Bee (Apr 15, 2013)

snl said:


> I've not lost a hive to mites since I started treating exclusively with OAV.


How long have you been using it exclusively?


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## snl (Nov 20, 2009)

mbc said:


> I'd read that an average of four days were spent phoretic after emerging before diving back in to some, about to be capped, brood- I'll try and remember where I read it and post a link.
> This part of the lifecycle has important implications for treatment regimes and we should try and be as precise as possible about it imho.


You are correct: here's the link: http://entnemdept.ufl.edu/creatures/misc/bees/varroa_mite.htm
When I stated that the mite's are ready to jump back into brood once they emerged, I did not mean overnite, just that they would do so within days...


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## snl (Nov 20, 2009)

Brad Bee said:


> How long have you been using it exclusively?


Three years, but I do so religiously. Right after I pull the supers, I vaporize 3 times, 5-7 days apart, then once again between Thanksgiving and Christmas. That regime with an occasional spring treatment before placing the supers works for me....


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## mbc (Mar 22, 2014)

Thank you snl, a different piece to the one I can partially recall, but for those with little patience the relevant passage in the link you posted is below:

"The phoretic period of the mite appears to contribute to the mite's reproductive ability. Although mites artificially transferred to brood cells immediately after they mature are able to reproduce, their reproductive rate is lower than that of mites undergoing a phoretic period. The phoretic period may last 4.5 to 11 days when brood is present in the hive or as long as five to six months during the winter when no brood is present in the hive. Consequently, female mites living when brood is present in the colony have an average life expectancy of 27 days, yet in the absence of brood, they may live for many months."


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## buzzleblast (Jan 16, 2014)

Lburou said:


> I found these pictures somewhere....Ostensibly showing before and after oxalic acid exposure. The proboscis would be the mouth part. HTH


I am a fan and active proponent of OAV, have seen positive results in my hives, and will continue to use it exclusively.
However, regarding those pictures, there is NO WAY they can get the exact same mite in the exact same position before a treatment and after. I'm calling BS. 
Aggravating, because I am already a proponent, and I would really love to see something that indicates the mechanics of the mites demise. Why would we need to 'gild the lily' by faking the effects?


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## shinbone (Jul 5, 2011)

Regarding the photomicrograph; hard to say for sure, but the background behind the "burned off" mouth parts looks "smudged" and lighter with a slightly different texture than the adjacent background, which raises in my mind the suspicion of a possibility of a Photoshop effort. I am not saying "for sure", it just looks a little "off" to me.

And, I use OAV with good results, so I am not pushing an anti-OAV agenda in questioning the photo.


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## Michael Bush (Aug 2, 2002)

>However, regarding those pictures, there is NO WAY they can get the exact same mite in the exact same position before a treatment and after.

Agreed.


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## ericweller (Jan 10, 2013)

Sorry to activate this thread but the photomicrographs are obviously doctored. If you look at the texture of the ground in each picture, they are exactly alike. Unless the two mite's pictures were taken in the exact same location, someone was having fun with Photoshop.


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## dsegrest (May 15, 2014)

Axtmann said:


> Believe it or not, you should not give an advice using OAV in spring. It's not a good idea, except if you are selling the vaporizer. The beginners think every is OK after the treatment, but most of the time, it is not.
> 
> Beginner
> Think about, if 95% of the mites hiding in closed cells, how long will it take and your hive is gone? If you have a mite problem in spring, you made a mistake last fall. Use a treatment that is recommended for the warmer temperatures and works even when bees have brood, like formic acid pads or thymol strips. Even cutting the drone brood during the year will reduce the mites not more than 50%, if you're lucky.
> There is always somebody with a different opinion, but this are my experiences.


I think this depends on the colony and the climate. I try to do a single shot treatment before the brood starts building up. We do not have a true broodless period in piedmont NC but there is not much brood in late February. I don't do the 3 treatments over 15 days like in the fall.


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## jwcarlson (Feb 14, 2014)

If you look at the "after" picture closely you can see the blurry areas where they scrubbed the stuff from the image. Makes it pretty obvious once you see some of it, the whole area sticks out like a sore thumb.


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