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A Device for Quick, Safe1 Oxalic Acid Vaporization
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Oxalic Acid Safety

At the recent ABA convention, Cor De Wit described his experimental set-up for using oxalic acid vaporization to control varroa.  I was so impressed, that I asked him for his slides and he obliged.  In fact, he drove to Edmonton, had them put onto a CD and sent them to me -- and he won't let me pay him for the effort.

At first, Cor tried the VARROX oxalic evaporator as designed and recommended, but encountered some problems:

Treatment took too much time per hive for commercial bee operations with hundreds or thousands of hives

Fumes were escaping out of the entrance and cracks in the hive, lowering efficacy and presenting a hazard

The low clearance of entrances in North American hives resulted in  poor circulation of fumes in the hive, and possible fire hazard.

Click on any thumbnail photo for a full-size view.

Here's the VARROX Verdampfer, used as designed. There is an obvious clearance problem.

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(The green carpet strip is to deter skunks).


Cor decided to use the best features of the device, but to improve on the method of use to increase convenience and efficacy, and to reduce hazards to the operator.  He built a  cart with automotive batteries and a fan, and developed a small sheet metal enclosure for the VARROX verdampfer. 

The enclosure has an inlet for the fan, a spout to fit easily into the hive entrance through the small hole in the reducer, and a filler funnel, into which the oxalic can be dropped onto the hotplate of the VARROX verdamfer.  A cork plugs the filler hole to prevent fumes escaping there when the fan is activated.  The boxes have legs and a handle to make it easy to swing one into place in front of each and have it stay it there during two minutes of the treatment.

A timer on the cart turns the fan off after two minutes. I think it controls the VARROX evaporator as well, but I'll have to ask and learn more about the details.

Here are some salient facts:

Oxalic acid (OA) is present in foods like rhubarb.

OA in food is dangerous in concentrated form, but apparently harmless and non-cumulative in small amounts.

OA vapour and the dust from the powder can be dangerous to humans if not properly handled.

Applied properly, OA seems harmless to bees.

OA is naturally found in beehives and honey

OA levels found in hives and honey did not seem to increase at all after OA vapour treatments.

Oxalic acid vaporization treatment is as effective around zero degrees C (freezing) as at higher temperatures

OA works best when there is little or no brood in the hives

In Alberta the most reliable broodless period begins in late October and November. 

Mean temperatures run just above zero in in late October and November.

We wrap out hives in October and November.

Note: Although Canadian authorities have not yet gotten around to verifying the work and making a formal approval, use of oxalic acid in beehives to treat for varroa has been extensively tested, and is approved in some of the fussiest European countries.

As with any treatment, there are advantages and disadvantages to this method.  This article is not meant to be a recommendation or an endorsement, but is merely presented to encourage understanding, further study, and, hopefully, early approval.

Oxalic Sublimation

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The cart in a yard with wrapped hives

A close-up view of the 12 volt fan.

Another view of the fan, showing the timer

Set up and ready for the crystals

Adding the oxalic acid crystals.  2 grams is the amount used.

The fan and verdamfer are actuated.  In two minutes the acid is evaporated and blown into the hive where it precipitates everywhere.

2002 | 2004 | 2008 | 2010 | Using Formic & Oxalic | Home

Using Formic & Oxalic Acids for treatment of Varroa & Tracheal Mites

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