# OAV treatment limits?



## Daniel Y (Sep 12, 2011)

Some do a 4th as a regular treatment. I do not recall hearing of a 5th. How many days between treatments?


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## RobA (Dec 18, 2014)

6 days and 7 days.


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## mgolden (Oct 26, 2011)

Have done as many as six times seven days a part. Kept seeing mite drop count higher than I liked. And I was also refining my application procedure with my homemade OAV tool.

Saw no adverse affects and hive continued on as if nothing happened.


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## enjambres (Jun 30, 2013)

If you used any six-day interval, then I wouldn't hesitate to do a fourth one because the shortened interval changes the just-barely-enough time to kill the newly hatched mites from the last pre-treatment started drone cells _total treatment period._

And any way the old folk-wisdom prescription (articulated by whom, I never found out) was four doses on five day intervals. So many of of us can attest that the cumulative pesticide exposure load of four doses did no harm.

But then I would wait at least a week and do a sugar roll to assess your mite load, before just adding more OA.

Enj.


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## DaisyNJ (Aug 3, 2015)

From what I understand, the goal is to cover the 21 day period - typical worker emergence, to target most phoretic mites. After that you really want to think about pro / cons of continuously applying same treatment.


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## Phoebee (Jan 29, 2014)

My OA instruction sheet is 130 miles away right now, but I'd say repeating treatments while brood is present is "off label." The official instructions are that it is for application while no brood is present, and that repeat treatments can harm the bees.

http://blog.brushymountainbeefarm.com/2015/09/oxalic-acid-faqs.html

"CAN YOU TREAT IN THE SUMMER?
While some studies say you can treat honey bees in the summer, there are too many variables that can cause issues during summer treatments. Summertime is usually when the hive is full of capped brood so it could take multiple treatments to reduce all the mites concealed with the brood. Continuous multiple treatments can affect the bees severely."


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## cervus (May 8, 2016)

It's not summer anymore.


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## Phoebee (Jan 29, 2014)

cervus said:


> It's not summer anymore.


My calendar says it is still summer (even though we're in winter prep). In any case, the bees still have brood, so OAV requires multiple treatments to be effective. My point is, the official labeling and instructions for this product say don't do it. I realize that long-term users of OAV were using it long before there was any labeling because it was just approved in the US this year.


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## Davisbees (Apr 24, 2009)

I use screen bottom boards on all of my hives and need to seal these up so i got a sheet of Masonite one eight thick and cut it to slide over the screen. Has anyone else ever used Masonite and did it work ok?


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## RobA (Dec 18, 2014)

DaisyNJ said:


> From what I understand, the goal is to cover the 21 day period - typical worker emergence, to target most phoretic mites. After that you really want to think about pro / cons of continuously applying same treatment.


The 21 day thing made me think - if I do 3 treatments 7 days apart that covers only 14 days. 4 treatments 7 days apart covers 21 days.


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## cervus (May 8, 2016)

Phoebee said:


> My calendar says it is still summer (even though we're in winter prep). In any case, the bees still have brood, so OAV requires multiple treatments to be effective. My point is, the official labeling and instructions for this product say don't do it. I realize that long-term users of OAV were using it long before there was any labeling because it was just approved in the US this year.


If it's still summer, can I continue wearing my white shoes? Yes, the label does say to use it late fall/early spring when *little to no brood is present*. The label goes on to say Oxalic Acid Dihydrate *might *damage bee brood. 

Both the label and Brushy Mtn's recommendations seem to be in direct contradiction to Mr.Oliver's observations: _"Dr. Ellis’s experience, anecdotal reports, and my own experience indicate that colonies can handle the recommended dosages well, even with multiple summer treatments."_(http://scientificbeekeeping.com/oxalic-acid-questions-answers-and-more-questions-part-1-of-2-parts/). 

Could be dribble, could be vaporization, could be both. I think the jury is still out. I need to treat when brood is present.


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## Phoebee (Jan 29, 2014)

Well, most of the beekeepers I know continue to wear white almost all year.

I can only speak for my bees, a VSH-based breed developed in Virginia that naturally do a pretty good job of keeping mites down. Grandma bee, now in her third summer, had three mites on her IPM board last weekend on a tray that had been in there for two months. I think she was last treated (with a fresh dose of formic acid) in 2014. So my luck with OAV may not be typical.

A treatment last winter when the hive was broodless seems to have wiped the nasty things out of one hive, which has been our strongest hive all year. Their drop is so low I get tired of looking. Realizing you don't want to go into fall with a high count and must do what you must do, I would suggest that getting in the habit of treating, per the label, in late fall or winter when the hive is broodless may yield delightful results the following summer.


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## cervus (May 8, 2016)

RobA said:


> The 21 day thing made me think - if I do 3 treatments 7 days apart that covers only 14 days. 4 treatments 7 days apart covers 21 days.


Three times probably accounts for the residual activity. I'm repeating treatments until my mite-drop counts indicate adequate control. Three treatments, 7 days apart didn't work this time.



Phoebee said:


> Well, most of the beekeepers I know continue to wear white almost all year.


 touche'


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## cervus (May 8, 2016)

Davisbees said:


> I use screen bottom boards on all of my hives and need to seal these up so i got a sheet of Masonite one eight thick and cut it to slide over the screen. Has anyone else ever used Masonite and did it work ok?


I just use coroplast. It's the material used to make those political signs that bloom all over during elections.


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## enjambres (Jun 30, 2013)

I wouldn't use plastic - or masonite- directly under the wand because of the heat.

I use rimless aluminum cookie sheets. But I think you could easily make something similar using roof flashing, bending the edges over to make it stiff enough to slide in easily.

RobA has correctly identified the weakness that I see in the 3 X/7 day interval labeling. It does only cover a period that barely ekes out enough days to hit the mites capped with drones the day before the first treatment. Because if you count the first treatment as Day 1, you treat again on Day 8, and again on Day 15. And then you're officially done. Even if you allow for some residual action, a day or two more is about all you could expect. And we routinely tell ourselves that if you've got treatment-protected honey supers overhead it's OK to remove the barriers almost right away, so how much residual effect could we expect if the honey is safe after only a short time? 

(BTW, the old folk-wisdom prescription: 4X/5 days isn't much better, either. Just one day longer, the final treatment is on the 16th day.

I spent a fair amount of time modeling this mathematically last winter and it's still a pretty shakey proposition using percent expected kill (high), expected emergence of mites that were previously capping-protected in the inter-treatment interval, repeat treatment percentage killed etc. No matter how you look at it, you get to a floor that doesn't seem like it would be all that effective. And yet, in practice it seems to work very well.

So despite being a "the label is the Law" kinda gal, I treat three times and repeat a sugar roll on the 7th day after the final treatment. If I'm not happy with the numbers (which I don't ever expect to be zero, but often they are low enough especially because I am also watching my sticky boards carefully at that point) I will do a fourth treatment and sugar roll _again_ of the seventh day after that. I have never felt the need to go farther (add a fifth treatment), partly because I usually only use OAV in the fall and I have the population dynamics (of both bees and mites) working with me at that point. And also because I expect to treat again in December, which is usually just a 7 or 8 weeks away.

I suppose you could call a fourth treatment, the first in a fresh series (that you abandoned after one dose). I use wood bleach so I've never seen the label of "real OAV", and therefore I don't know if there is a specified treatment blackout period following one complete cycle.

YMMV,
Enj.


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## snl (Nov 20, 2009)

OA will continue to kill until it is carried out of the hives by bees in about 3 days (who see it as trash)...
Day 1 - Most phoretic mites killed.
Day 2 - Many Emerging mites killed (yes, some not killed on day 1 will enter brood about to be capped)
Day 3 - Many Emerging mites killed (yes, some not killed on day 1 will enter brood about to be capped)
Day 4 - Mites emerge with brood .... enter phoretic stage
Day 5 - Mites emerge with brood .... enter phoretic stage
Day 6 - Mites emerge with brood .... enter phoretic stage
Day 7 - Next treatment - most phoretic mites killed prior to entering brood about to be capped.

3 Treatments cover the brood cycle... You will never get all mites during brood rearing. But......... you'll knock the devil out of them until you get them all during the broodless period.
Now is the a great time to treat. You want healthy bees raising health winter bees ........ who will keep the hive alive.


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## DaisyNJ (Aug 3, 2015)

Yep and I saw the math as... 

Treatment 1 - Day 8th (oldest open larva before being capped). Every hatched bee upto this day will be treated. 
Treatment 2 - Day 15th 
Treatment 3 - Day 22nd (anything about to be capped on Treatment day 1 emerge the day before or same day)

So pretty much every bee is treated in that cycle.


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## texanbelchers (Aug 4, 2014)

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Broodless .... What is broodless???? That is when I know I have queen problems!!

Like many other things in beekeeping, the focus is on the cooler climates. Brushy Mountain also doesn't differentiate between OAD and OAV, but these impact the hive differently.

From: http://scientificbeekeeping.com/oxalic-acid-heat-vaporization-and-other-methods-part-2-of-2-parts/
There are two problems associated with OA dribble: (1) it requires opening the colonies for the fall/winter treatment, and (2) there are issues of bee toxicity and depressed broodrearing due to bees ingesting some of the syrup. Both these issues can be circumvented by applying the acid in vapor form.*

Does vaporization hurt the bees?*
Radetzki didn’t note increased bee mortality after winter treatment. Heinz Kaemmerer of Heilyser Technology Ltd. says: “We treated several colonies for 3 months during winter, once a week with the vaporizer and all colonies survived.” “With brood, colonies can be treated with the right amount of OA 3 to 4 times, a week apart; there is no harm to bees, queen or brood.” Medhat Nasr confirms that vaporized oxalic is very gentle to the bees.


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## MichiganMike (Mar 25, 2014)

Generally from egg to capping is 9 days and drones are capped for 15 days. All capped brood hatches about 7 days before the third treatment. 23 days worth of uncapped brood is exposed to treatment. I treat immediately after my early August harvest 7x4 that exposes 30 days worth of uncapped brood and in October 7x3 and once in December if temperature permits. I am not aware of any ill effects on the bees.


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## mgstei1 (Jan 11, 2014)

Like Texanbelchers is saying, the europeans are the experts and know the OAV treatments way better than Americans. They have the experience with OA both wet and dry..
Ive been treating in the fall for 3 years now in November, rain or shine or heat or cold once a week. It works well coming out of winter into the spring. I dont do mite counts any longer either. I treat 4 times a year and watch the drop. Only in the fall do I do more than 1-2 treatments a week apart. Just like cows, treat. Dont wait until they keel over cause then its too late.


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## enjambres (Jun 30, 2013)

Um, some people are confusing the number of times you're treating (three or four) with the cumulative sum of the elapsed intervals between treatments, i.e  one less interval than the total number of treatments.

So for three treatments, you have three treatment days, and two six-day intervals between them.

For four treatments, it's four treatment days, plus three intervals.

Look at your hand: you have five fingers, and four spaces between them.

It's easy to make the mistake of thinking three treatments at seven day intervals takes 21 days, but they only take 15 days (four at seven equals 22 days).

Plus according to SNL, maybe three days tacked on the end before it's all out of the hive, and no longer effective.

And that's the problem, because the darned drones -which have the majority of the mites entombed with them under the cappings - take 14 days to emerge (plus or minus a day). The three-dose just barely covers them. That's why I liked the old four-dose plan better. It gave a better margin. 

Enj.


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## Daniel Y (Sep 12, 2011)

Phoebee said:


> My OA instruction sheet is 130 miles away right now, but I'd say repeating treatments while brood is present is "off label." The official instructions are that it is for application while no brood is present, and that repeat treatments can harm the bees.
> 
> QUOTE]
> 
> Not true, from the label. "You can treat in the spring and summer but research shows that Oxalic works best in the fall/winter." It also mentions the reduced effectiveness of treating when there is capped brood but is not forbidden. The only time OA is forbidden is when there is marketable honey on the hive.


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## BernhardHeuvel (Mar 13, 2013)

A friend tested the limits...and this is what he found.

Question: How many times can you use oxalic acid vapor before you can see damage to the bees? 

Answer: He treated 30 times in a row, three days apart, 1 g oxalic acid. 

Result: Bees wintered just fine with a huge number of bees. No damage neither to the bees nor to the brood could be observed. 

In summer you need a different strategy when you see a high mite population and brood is still present. Use 2 g oxalic acid for the initial/first vaporizing. If you have a heavy mite load, treat every three days for six or seven times. With a more normal mite level, three/four times seven days apart will do. If unsure, repeat treatment for another round. 

You can't hurt the bees with proper sublimation. That is the good thing about it. In a field test (1,600 hives involved) it has been found that vaporization of 5 g does damage a portion of the bees. Oxalic acid has the same effect to the mites (high kill rates) from 0.5 g on to 5 g. The average used is 1 g oxalic acid to make sure. Theoretically 0.5 g would be enough. But if your device does burn the oxalic acid too much, you be safer using 1 g. That is why this is recommended that way.


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