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I treated my hives for mites using an oxalic acid vaporizer in October. They were all two deeps worth, so I used two grams. I had read that in order to be effective it was important to make sure that the hive was treated multiple times to ensure that all stages of brood rearing were covered. I still ended up with some pretty bad mite damage. Also, it was mentioned that OA kills the bees. This is something that I had not understood before. I was under the impression that OA was safe for the bees. It was suggested that by applying multiple times, I may have actually killed my bees instead of or in addition to the mites.

So... I have a couple of questions.

1. Is OA safe for the bees, or can it kill them?
2. Should it be applied multiple times (I did it every Saturday for three weeks consecutively).
3. If I should continue using the vaporizer, when and how often should I treat?
4. If I should abandon the vaporizer, what mite treatment is most effective in correlation to ease of use and expense?

OK... So it was more than a couple of questions! :D
 

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Tristan,
I believe you are confusing the 2 types of Oxalic application methods, OA mixed with sugar syrup (dribble method) should only be applied 1 time every 6 months or bee death will occur. OAV or (Oxalic Acid Vapor) can be applied one time a week for 3 or 4 weeks without harming the bees.

I cannot answer your last question, I like OAV and it is the only type of treatment I have ever used.
 

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The general consensus is that the dribble method (oxalic in sugar solution) is hard on bees, and does result in significant mortality to the point that multiple treatments during the year should be avoided. Vaporizing, on the other hand, is much gentler on the bees.

See Randy Oliver's article: http://scientificbeekeeping.com/oxalic-acid-heat-vaporization-and-other-methods-part-2-of-2-parts/

References are made in this article to several sources that indicate that if properly applied, there is little to no increase in mortality from vaporizing oxalic acid. Heilyser, one of the manufacturers of vaporizers, treated a hive weekly for three months with no observed ill effects. Michael Bush points out that the very low pH in the hive from the oxalic acid will have an impact on the other potentially beneficial microbes that live in the hive. Projecting from that, even if it does a good job of killing varroa and not killing bees, it's still probably a good idea not to over treat with oxalic acid. I would tend to think that twice a year would be sufficient (each course being three treatments a week apart to ensure smacking the mites that were in capped brood).

I have read experiences of those who have observed bee mortality from vaporizing oxalic acid, but in each case that I'm aware of, at least one of two contributing factors was present: 1) the dose was too large (don't exceed approximately 1 gram per deep, which works out to 2 grams per 3 mediums), or 2) the method of application was with a pipe heated with a propane torch. The problem with the pipe is that it is nearly impossible to consistently control the vaporization of the oxalic acid. At 315F, the oxalic acid starts to sublimate (turn from crystals to vapor), but at 372F it decomposes to carbon monoxide and formic acid. Propane torches can easily produce 2,000F, so if the pipe gets too hot, the oxalic acid will decompose instead of vaporize, and although the bees aren't likely to be bothered by the formic acid (it's much weaker per gram than oxalic) they will definitely be bothered by the carbon monoxide. To avoid that altogether, it's a much better idea to use an electric vaporizer that heats the oxalic acid crystals much more slowly, allowing them to evenly vaporize before the temperature range is exceeded.

I treated my own three hives last October with three consecutive weekly treatments after measuring high mite counts, and it definitely helped- the mite drop after treatment was enormous, and subsequent powdered sugar roll mite count yielded near zero, and all three hives survived overwinter and have started a strong buildup for spring. (two of them actually produced a few more frames of eucalyptus honey over the winter, flying more than normal with the nice weather we've been having)

Hope that helps!
 

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So... I have a couple of questions.OK... So it was more than a couple of questions! :D
1. Is OA safe for the bees, or can it kill them?
Answer: OA is safe for bees in a vaporized form and when used as directed.

2. Should it be applied multiple times (I did it every Saturday for three weeks consecutively).
Answer: Once, maybe twice is the recommended treatment.

3. If I should continue using the vaporizer, when and how often should I treat?
Answer. Since you've already used it multiple times, I would not treat again.

4. If I should abandon the vaporizer, what mite treatment is most effective in correlation to ease of use and expense?

Answer. I like MAQS altho it is temperature dependent. I only use one pad per treatment vs the recommended two. I have not found that it harms my queens or causes supercedure. To each his own.
 

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tristan,

You may want to consider doing the treatments a little earlier in the season. I don't know what your climate is like where you are but the mite load may have overwhelmed the colony in August or September. By October it may have been too late, the damage was already done.

There are many beekeepers around the world who successfully perform multiple OA treatments in the Fall with great success, and no crippling harmful effects on the bees. Timing for treatments is important for best results.
 

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I have found that one treatment is not sufficient and I treat 3-4 times a week or so apart with no noticeable damage to the bees or brood.
I too have found that's the case......... but once, maybe twice is the recommended treatment.......
 
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