View Full Version : Hazards of Oxalic Acid Use in Bee Hives

03-03-2006, 08:44 PM
Was over at a neighbours the other day, and we had drifted on to the subject of Oxalic Acid use for mite control.

Got talking about vapourizing oxalic acid and some of the new devices being manufactured to dispense the substance into the hives for treatment.

Before vuisiting him I was completely committed to buying the new vapourizor blower comming onto the market, but I have to say after speaking to him of his take on the issue, I am now a bit leary of treating via vapourizing, and leaning more towards the drench method.

His main concern was the hazard the OA posed on the applicator. In fact not only at the time of application, but also subsequent hive visits after. He mentioned that there have been experiences with the vapours condensing and forming crystals on the top bars and innercovers. His concern was the hazard those OA crystals had on the beekeeper when being scrapped off in later visits.

I realize the health hazards of OA, and figured I can manage that risk with proper equipment at the time of applications, but if his learned experiences are true, there is an extreem potential health hazard looming after oxalic acid treatment which I havent heard anyone here mention yet.

Any suggestions?

03-03-2006, 09:19 PM
Hi Ian,

interesting point
I've used OA a couple of time on my one hive so my experience doesn't count for much, but before I used it on the bee's I did experiment with it by vaporising in an empty hive body in the yard with a piece of plexiglass over the top
it does coat everything with quite a bit of residue
my main concern was breathing the vapor so I bought a JB200 so I can plug it in and walk away, but the idea of this residue in the hive is something to think about
my first thought would be that the bees would clean it up but I certainly don't have any backing for that
I have seen studies that indicate that analysis of wax and honey done some time after treatment show no elevated levels
with my experiment in the yard it left the ground looking like we had a heavy frost
I'm hoping small cell will aleviate me from such concerns smile.gif


03-03-2006, 09:28 PM
>>my first thought would be that the bees would clean it

I wonder if they would clean it up, or propolis over.

03-03-2006, 10:11 PM
Here's an interesting article I read just last night. I too am concerned about the safety of breathing this stuff after treatment. I don't think this study addresses the "leftover" OA, back in crystalline form inside the hive, but it is still relevant to this discussion. Good pics too.


George Fergusson
03-04-2006, 07:19 AM
Likewise, kenpkr. Here's a site with information about residual OA in hives from vaporization:



David Stewart
03-04-2006, 08:10 AM
Someone here (I forget the author) posted a comment some time back which stuck in my head. As I recall the post went
-They don't call it a crack pipe for nothing-

I had to resort to chemical treatment late last summer and hated doing it. May have been too late in the year and I may still lose this hive, but there has got to be a better way until I can complete the transition to small cell.

Ben Brewcat
03-04-2006, 09:40 AM
I just used a JB200 for the 1st time and Holy Slick Slayer of Mites Batman! Nice to walk away for sure; duct tape over entrance. For the residue, I suspect that washing your hands before rubbing your eyes or picking your nose would be pretty effective, and after a week or two I suspect the bees walking around, cleaning and propolizing would ameliorate the risk. Last year's crackpipe uses I did note surface residues, but much abated after a couple weeks.

03-04-2006, 03:26 PM
>> did note surface residues, but much abated after a couple weeks.

Its those surface residues that I am concerned about. I am afraid of breathing in OA dust while working and scraping the frames and box.

This stuff will cause serious organ damage if your exposed.

George Fergusson
03-04-2006, 05:05 PM
Ian, that's one of the main reasons I intend to really push drone comb trapping this coming season. I'll use OA if I have to, and I'm sure I'll have to, but I don't want it to become Standard Operating Procedure.

Robert Hawkins
03-04-2006, 07:39 PM
<This stuff will cause serious organ damage if your exposed.>

If you have to wash it off your hands, it's too late. You'er exposed. And you will die in approx. twelve years.

I'm not joking folks. This is a serious health hazard and not worth using.


Michael Bush
03-04-2006, 07:46 PM
>This stuff will cause serious organ damage if your exposed.

But you are exposed. Everytime you eat just about anything. Honey. Rhubarb. Asparagus...

The residue is quickly cleaned up by the bees.

My concern would be making sure you don't breath the vapors.

Elmar Mook
03-05-2006, 02:34 AM
If you do't have to treat hudreds of hives ad are afraid of OA (maybe we should, actually), try lactic acid! It's an approved food additive!!

luck, Elmar

03-05-2006, 08:53 AM
Like other treatments it is important not to use them unless mite counts show they are needed.

What is the vaporization temp of OA?

George Fergusson
03-05-2006, 08:59 AM
150 C sticks in my memory, which is 302 F.

03-05-2006, 01:58 PM
>>But you are exposed. Everytime you eat just about anything. Honey. Rhubarb. Asparagus...

Its the higher concentrated exposures that cause harm

>>The residue is quickly cleaned up by the bees.
>>My concern would be making sure you don't breath the vapors.

Has there been any studdy in looking into the residue hazard within the hive after application? Is there or isnt there a hazard in the hive after application with the vapourizor?

If this is incorperated into any beekeeping operation, there will be continual OA exposure to the beekeeper, be it an accidental breath of vapours from treatment, to constant minimal contant of dust residue with in the hive. Is that exposure going to harm my health later down the road?
Perhaps the drizle method is the better of the two treatment options afterall,.

03-05-2006, 02:01 PM
>> I intend to really push drone comb trapping this coming season

Cool, very effective method of reducing mite populations in your hives,

Alot of work involved, and just not practical on a larger scale operation.

George Fergusson
03-05-2006, 03:03 PM
>Has there been any studdy in looking into the residue hazard within the hive after application?

Yes, if not the hazard part at least the residue part- the link I posted above, copied here:


To be honest, I need to review it again myself. I last read it last summer.

>Alot of work involved, and just not practical on a larger scale operation.

Granted. At what size do you see it becoming impractical and why? Is it just the labor involved?

Toni Bee
03-05-2006, 04:42 PM
I'll confess up front that I have already used vaporized oxalic, and was not thrilled at the idea, but you guys have scared the daylights out of me (btw not hard to do!) so I looked up a couple of things.

The study George linked to compares the exposure of beekeepers handling frame residue to that of a housewife chopping rhubarb, and finds the housewife has at least 25 times more exposure to oxalic acid.

On http://www.rhubarbinfo.com/rhubarb-poison.html, the figure of 25 grams of ingested oxalic for a 145 pound person is cited as the fatal threshold. That's more than 8 treatment doses.

So the main risk appears NOT to be handling or eating the stuff, but breathing it.

Finally, the idea that I could die a decade from now from breathing the stuff seems unsupported. Instead, I could die right now, if I mess up. On down the line, I could get kidney stones, which would suck but probably not kill me.

So this method still has extreme drawbacks, but it kills mites like crazy. You must not mess around when handling this stuff, and I support the idea that other IPM approaches are much better, if labor intensive.

03-05-2006, 07:40 PM
Hi Guys,

Risk assessment is a very basic fundamental before selecting any kind of poison. And that's just what a beekeeper is looking for when he choses to commit insecticide, a poison!

Oxalic acid is one of the most benign, yet effective, poisons a beekeeper can choose. And, unlike the strips, it's one of the most obnoxious which is one of it's greatest attributes. A person might inadvertantly breath a small amount of the vapor. But, unless the person is unconsious or trapped, I can guarentee that he won't stick around for even a small second breath of it. And it would take quite a few breaths before any damage would be done. And that would be way below any lethal limits.

You can't be unknowningly exposed to oxalic even at the smallest dosages!

Appropriate precautions are easy to take and should be taken by anyone using it.

It's not scary stuff, it's just oxalic. Remember some people use it as a wood/metal bleach without much precaution at all.

When I generated my webpage concerning it, I started with a heavy focus on saftey knowing that it would reach a general audience. And a few of those people would never even read the writeup. But would only look at the pictures. And some of those wouldn't have any experience with industrial chemicals, or agriculture, or household chemicals, or any chemistry class or much practical experience. It's possible for such a person to do something very stupid with oxalic. I tried to even cover that possibility in the writeup. But for anyone with any kind of experience noted above, using oxalic is no problem.

The residue question was addressed early on with the bee houses in Europe. It was recommended that the houses be aired for 24 hours after hives were treated.

If lumps and clumps of oxalic are deposited in a hive, something has gone wrong during the application. The application should produce a smoke like product which coats the interior of the hive.


[ March 05, 2006, 08:58 PM: Message edited by: B Wrangler ]

03-06-2006, 07:51 AM
>>The application should produce a smoke like product which coats the interior of the hive.

Thanks Dennis, its that coating of the hive, and the crystalization of the vapours along frame tops and innner covers that I am concerned about here. Later scraping and OA dust exposure to the respitory system. An exposure that the beekeeper would be totally unaware. That "unknowningly exposure to oxalic even at the smallest dosage" after each and every treatment of the stuff concerns me.

Your right, hazards must be considered before applicating any treatment, organic or not!
Its the assumtion organic treatments pose no health threat that concerns me. Just because it is food grade and a natural substance, doesnt make it safe to be exposed to.
Alot of these organic methods are used with that assumption without alot of studdy on the use of the product itself.

>The residue question was addressed early on with the bee houses in Europe.

So they determined the residue of the vapourized OA was next to nil? Did they notice any variations between applications, and between seasons when applicated?

[ March 06, 2006, 09:04 AM: Message edited by: Ian ]

03-06-2006, 07:53 AM
Well put Dennis.

I am considering OA as only an emergency treatment fall back for my small cell colonies.

Seems the least dangerous and least harmful of the "poison" treatments.

Like the drone trapping concept. But is I run 500 colonies there just isn't time.

03-06-2006, 07:59 AM
George, I cant get your link to translate. Perhaps you can summerize it to me? Sorry for the bother.

>>Granted. At what size do you see it becoming impractical and why? Is it just the labor involved?

Well, I am running 400 hives. To rotate the drone brood out every 20 or so days on 400 hundred hives, lets say for 4 cycles, would mean, well alot of work.

Our guys up here have experimented with trying to lour the mites using the same pharmones drone brood release into "mite traps". The idea was to exploit the drone brood removal idea, and make it somehow feasable to apply it large scale. It was eventually mothballed, but the idea still looms.

03-06-2006, 08:07 AM
That sounds like an interesting concept Ian. Hope someone picks it up again.

Ben Brewcat
03-06-2006, 01:11 PM
Wonderful link; I'm much reassured. I stand 50 feet away at my car when I clamp onto the battery to start vaporization, and come back 15 mins after disconnecting the electric element.

Dave W
03-06-2006, 01:44 PM
The following is from my personal notes.

OXALIC ACID - CAS # 6153-56-6 Dehydrate (144-62-7 Anhydrous)

Chemical Class - Organic acid

Description - Oxalic Acid dehydrate (OA), is a white (colorless) crystal, granule or powder. It is used in solutions for a wide range of industrial processes. It’s slightly soluble in water. Corrosive to metals. Poison. OA reacts explosively w/ strong oxidizing materials and some silver compounds. Incompatible w/ alkalis, chlorites, hypochlorities, furfuryl alcohol, steel, moisture. Avoid contact w/ metals. Carbon dioxide and carbon monoxide form when heated to decomposition. Also forms formic acid [http://www.jbaker.com/msds/englishhtml/o6044.htm] (1% - 10mg/1g of vaporized OA) [http://www.mellifera.de/Engli2.pdf - Accessed 7/13/04].

When heating, about half (46%) of OA decomposes into harmless carbon dioxide and water. Other half (54%) vaporizes and forms fine drops and dusts of OA that precipitates everywhere in hive. Because of this even distribution of fine particles, high and consistent efficacy against Varroa mites is possible [http://www.mellifera.de/Engli2.pdf - Accessed 7/13/04].

OA is a naturally occurring component of our nourishment. It can be found in almost every plant we eat and is a natural component of honey (0.02 to 2 g/kg). Rhubarb becomes sour because of 2.6 to 6.2 grams of OA that is contained in each kilogram of fresh plant [http://www.mellifera.de/Engli2.pdf].

CHEMICAL NAME - Ethanedioic Acid MELTING POINT - 219.2oF - 222.8oF
SYNONYMS - Ethandionic Acid, Aktisal, Aquisal BOILING POINT - 300 - 320F

Health Effects - Pure OA is an unhealthy, toxic and corrosive substance [http://www.mellifera.de/Engli2.pdf - Accessed 7/13/04]. Can cause severe irritation and burns of nose, throat, and respiratory tract, causing coughing, wheezing and/or shortness of breath. Exposure can cause headache, vomiting, stomach pain, weakness, seizures, coma and death. May cause nausea, severe gastroenteritis and vomiting, shock, and convulsions. May cause renal damage, as evidenced by bloody urine.

Human Fatal dose (estimated) - 5 to 15 grams [Source???] 15 to 30 grams
[http://www.cdc.gov/niosh/idlh/144627.html]. May be absorbed through skin. Can cause severe irritation, possible skin burns. OA is an eye irritant, may produce corrosive effects. Very destructive of mucous membranes. May cause congenital malformation in fetus. May damage kidneys and cause kidney stones. May affect nervous system.

Lethal Dose to kill 50% (LD50) - Rats: 375mg/kg (oral).

Beekeeper Exposure - Special safety precautions for the beekeeper are necessary, as w/ other products for Varroa control. When preparing solution for spraying, trickling or vaporizing OA crystals do NOT inhale dust. Use protective mask (FFP 3 S/L), gloves and protective glasses. Mask should be worn during treatment [http://www.mellifera.de/Engli2.pdf - Accessed 7/13/04]. Colonies in a beehouse must be treated from outside, and beehouse must be well ventilated during and after treatment [http://www.mellifera.de/engl2.htm-Accessed 2/3/05].

A study at the Institute of Occupational and Social Medicine, University of Tubingen, Germany has determined (while spraying or evaporating OA) that beekeeper exposure is below existing exposure limits for OA in the air at work place. There is no risk to the health of apiarist
[www.apis.admin.ch/en/krankheiten/docs/saeuren/os_anwendersicherheit_e.pdf] (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/os_anwendersicherheit_e.pdf]).

When cutting rhubarb, exposure to OA is 25 times higher than beekeepers’ exposure to residues on frames after vaporizing OA [http://www.mellifera.de/Engli2.pdf - Accessed 7/13/04].

Regulation by OSHA (cited by ACGIH, DOT, NIOSH and NFPA) requires OA to be on the Hazardous Substance List.

Registration – The American Bee Federation (ABF) directors have decided to pursue the registration of oxalic acid for treatment of V-mites [ABJ, 10/05, p782]. (Canadian approval announced in ABJ, 11/05, p864. See http://www.honeycouncil.ca/users/folder.asp?FolderID=876&nID=512.) Oxalic acid is NOT approved for use in the US [ABJ, 7/04, p475].

Testing of OA in dry vs. humid climates, and colder climates by Diana Sammataro, Carl Hayden HB Research Center, Tucson, has been funded (Spring 05 - Spring 06) by the National Honey Board [ABJ, 4/05, p271].

Austria was first (Oct 2001[http://www.mellifera.de/Engli2.pdf-Accessed 7/31/04]) to officially approve OA evaporation method [http://www.mellifera.de/engl2.htm-Accessed 2/05]. Oxalic acid is in widespread use in Europe because of its ease of application, high efficiency and low cost. A substantial amount of data exists on OA as a mite control substance. Unlikely that a chemical manufacturer would be interested in registering product because of its low cost as a generic.

Residue - In the year 2000, after vaporizing OA, honey showed an OA content between 22.8 and 37.7 mg/kg. Natural concentration of OA (determined by Franco Mutinelli et al, l’acido ossalico nella lotta alla varroasi, L’ape) varies from 20 to 400 mg/kg of honey [http://www.mellifera.de/engl2.htm-Accessed 2/05], 0.02 to 2 g/kg [http://www.mellifera.de/Engli2.pdf]. Use of oxalic acid in autumn does not increase concentration of OA in honey the next season114. Can therefore be used in autumn without affecting honey quality11.

Maximum Residue Level (MRL) - No maximum limit exist for oxalic acid residue in honey. According to European honey standards, honey may have up to 50 milli equivalents of free acids
[www.apis.admin.ch/en/krankheiten/docs/saeuren/mrl_bienenzeitung_e.pdf] (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/mrl_bienenzeitung_e.pdf]).

Use of oxalic acid as a miticide can leave taste residues in honey. A taste threshold of 400 - 900ppm (depending on honey aroma and taste) has been set by the Swiss, does not exceed worldwide MRL for organic acid in honey of 40 milli equivalent (meq) acid/kg11.

Resistance - No reports of resistance have been made. It is suggested that Varroa will not develop resistance to organic acids since they are a natural part of the metabolism of all organisms and cannot be rendered harmless through enzymatic effects50.

Storage -Store in a tightly closed container in a cool, well-ventilated area away from heat, moisture and incompatibilities.

Disposal - Unused chemical should be taken to an approved chemical waste disposal facility.

Source / Cost - Generic OA is commonly used as a wood bleach.
• Lowe’s, 12 oz wt (1 pint) $4.98 [Jan 04].
(2 cups = 1 pint, 16 tbl = 1 cup, 6 half-tsp. = 1 tbl, hence 2x16x6 = 192 half-tsp.
1 oz wt = 28.35 grams, hence 28.35x12 = 340.2 / 192 = 1.77 g per 1/2 teaspoon)

APPLICATION - Oxalic acid is only effective when colonies are broodless, and during broodless periods, control is excellent. Oxalic acid needs to be combined w/ other treatment methods when brood is present [BC, 3/06, p38]. Can be applied by evaporation, dripping (trickling) or spraying
[www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf] (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf]).

Winter treatment is extremely important because the mites that are destroyed constitute the basis for next year’s population. These mites have either survived autumn treatment or entered colony by re-invasion [Source???]. During the broodless period, all surviving mites are found on the bees. An efficient treatment during this time can significantly reduce the Varroa “kick-off” population for the coming season and further control measures will not be needed until summer of the coming year [www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf) - Accessed 1/19/05].

1) EVAPORATION method uses OA crystals, which are heated until they melt and boils into a vapor. The fumes penetrate hive and kills Varroa mites. First (???) used in the Soviet Union, where OA vapors are created outside hive and blown into colony [http://www.mellifera.de/engl2.htm-Accessed 2/05]. In-hive evaporation method developed by Mellifera e.V. Vereinigung für wesensgemässe Bienenhaltung, uses a small 12v (car battery) device inserted into hive entrance [http://www.mellifera.de/engl2.htm-Accessed 2/3/05]. See Proprietary Products.

A simple, cheap, homemade applicator / dispenser / vaporizer can be created using pipefittings, see http://bwrangler.litarium.com/varroa-blaster/. (http://www.geocities.com/usbwrangler/oxal.htm.) Uses 1/2 teaspoon of powder.
[Michael Bush - http://www.beesource.com/ubb/Forum2/HTML/001283.html].
• Applied once per treatment.
• Do NOT use during honey flow. [http://www.mellifera.de/engl2.htm].
• Withdrawal Period - ???
• Can be used during winter. Mid to late November (about 50OF) [www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf) - Accessed 1/19/05].
Tests applied about Nov 25 and about Jan 8 [http://www.mellifera.de/engl2.htm-Accessed 2/05].
• Second treatment should be applied about 2 wks after first, IF brood is present (or uncertain) OR if mite load is high [http://www.mellifera.de/engl2.htm-Accessed 2/05].
• Temperature - Ambient temperature NOT critical [Source???]. Tested between 35.6°F (2°C) and 60.8°F (16°C) [http://www.mellifera.de/engl2.htm-Accessed 2/3/05].
• Seal colony shut for 10 minutes [BC, 3/06, p38]. Close hive entrance during and for 15 minutes after treatment [http://www.mellifera.de/engl2.htm-Accessed 2/05].
• Can be used to treat nucs [http://www.mellifera.de/engl2.htm-Accessed 2/05].
• Labor - 8 minutes per hive [www.apis.admin.ch/en/krankheiten/docs/saeuren/os_anwendersicherheit_e.pdf-Accessed (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/os_anwendersicherheit_e.pdf-Accessed) 1/19/05].
• Cost per Treatment - $0.03 ($4.98 / 192 half-teaspoon [DLW])

Method #1 - BROODLESS in FALL - Treat 2 times, 2 wks apart [Michael Bush, http://www.beesource.com/ubb/Forum3/HTML/000217.html].

Method #2 - BROOD PRESENT - Treat 4 times, 7 days apart [Axtmann, http://www.beesource.com/ubb/Forum3/HTML/000217.html].
Move all capped brood (w/ bees) into separate super outside original hive and allow (existing) queen to lay on empty comb. All workers will fly back to (existing) queen, only young bees will remain w/ brood. Cut out queen cells started in separate super (capped brood) and treat w/ OA 3 times, 5 to 7 days apart. Treat original hive 1 or 2 times. After 21 days (when all brood has hatched), combine super (w/ young bees and queenless) to original hive (w/ queen) w/ honey super between [Herbert Axtmann, http://www.beesource.com/ubb/Forum3/HTML/000183.html - Accessed 4/23/04].

Effectiveness - 97% w/ VarroxR Vaporizer [http:www.imkerei-technik.de/varrox_verdampfer.htm (http://www.imkerei-technik.de/varrox_verdampfer.htm) - Accessed 7/13/04].
Single treatment = 95% [http://www.mellifera.de/engl2.htm-Accessed 2/05].
Effectiveness lower (75-100%) in Dadant hives [http://www.mellifera.de/engl2.htm-Accessed 2/05].
Effectiveness about the same for temperatures between 35.6°F (2°C) and 60.8°F (16°C) [http://www.mellifera.de/engl2.htm-Accessed 2/3/05].

Monitoring Results - Evaporation method is slower (to kill mites) than other OA methods.
One day after treatment, only 10% of total mites killed are found on hive bottom. After 1 week, 80% are killed. To determine exact number of dead V-mites, count mites for a period of 3 wks. [www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf) - Accessed 1/19/05].
Mite drop increases 270% from day 1 to day 8, but increasing only 18% over next 36 days. Oxalic acid kills mites for at least 44 days (6.3 wks) - see http://www.mellifera.de/engl2.htm (Accessed 2/3/05), Figure 2.

Adverse Effects - Conflicting reports to OA effects on bees range from no deleterious effect to impaired queen performance and poor overwintering success [ABJ, 6/04, p479]. Winter treatments can lead to harmful effects on the bees, when dosages are too high. Trials show that a correctly dosed, ONCE-ONLY treatment w/ OA (spray, drip or evaporation???) is well tolerated by the bees. Dead bees at hive entrance or in hive is not pertinent, because bees which die as a result of overdose of OA, are not found in the hive or near by. It is likely that these bees leave the hive and do not return [www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf) - Accessed 1/19/05]. Less than 200 dead bees (on hive bottom) were counted over a 5-week period following vapor treatment and double the mount of OA did not cause a higher deadfall. Average winter deadfall of untreated colonies was near 250 during same period [http://www.mellifera.de/engl2.htm-Accessed 2/05].

2) DRIP (trickle) treatment w/ a solution of sugar and 5% oxalic acid has been found to be highly effective in colonies without brood [ABJ, 8/05, p672]. This method is simple, quick, cheap and very effective in broodless colonies [Source?]. Trickling requires double brood chamber colonies to be cracked apart in cold weather [BC, 3/06, p38].
• Do NOT use during honey flow. Do not apply OA when honey supers are on hives, or during nectar flows if honey is to be extracted for human use [http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/guidelines/control.htm – p97, Accessed 8/1/05]. Apply any time as needed [Source???]
• Withdrawal Period - ???
• Can be used during winter. Outside temperature is not important, although the solution can chill the bees at low temperatures (below 32F) [http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/guidelines/control.htm – p98, Accessed 8/1/05].
• Labor - 1 minute per colony [ABJ, 6/04, p476]. Trickling requires the least amount of time and is easiest to apply [www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf (http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osbienenvertraeglichkeit2003_e.pdf) - Accessed 1/19/05].

Mode of Action - When consumed (solution [DLW,12/05]) by bees, probably acts as a protoplasmic poison by acidifying host bee’s hemolymph [ABJ, 6/04, p479].
• Because OA works through contact, ambient temperature is not critical. Mode of action appears to be low pH of OA solution116.

Prepare Solution – Several OA formulations have been tested in Europe. Variable concentrations of OA (1.8-4.5%) are produced by dissolving OA in sucrose solutions (0-60%). Volume used varies depending on bee colony size and strength (30-50 ml/colony) [ABJ, 6/05, p475].

Crystal form of OA only contains 71.4% OA. It is important to use this factor when preparing solutions. To determine the percentage (weight/volume) of OA in a syrup solution, divide the actual amount of OA (weight of OA x 0.714) by total volume of sugar solution. [http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/guidelines/control.htm – p97, Accessed 8/1/05]. (Example: 75 g of OA x 0.714 = 53.55 / 1.67 = 32.06 or 3.2% [DLW, 12/05])
• Mix 1 liter of water w/ 1 kg of sugar. Add 75 g of oxalic acid dehydrate. Mix thoroughly. Makes about 1.67 liters [http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/guidelines/control.htm – p97, Accessed 8/1/05]. (Produces a 3.2% solution [DLW, 12/05)
• Add 44.8 g (1.6 oz) oxalic acid dehydrate (99% purity; 71.4% oxalic acid) to 1 liter (ca. 1 qt) of a 50% sucrose solution (w/v) [ABJ, 6/05, p476]. (Produces a 4.5% solution [DLW, 12/05])

Amount to Use
• Use 5 ml of sugar syrup mixture per frame of bees (100% bee coverage [DLW,12/05) [http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/guidelines/control.htm – p97, Accessed 8/1/05].
• 5 ml (0.15 oz) of a 3.2% oxalic acid solution per frame [ABJ, 6/05, p476].

Method #1 –
Trickle oxalic acid solution directly onto bees between frames using a large syringe at a rate of 0.15 oz. (5 ml) of solution per frame. In 2-story colony, trickle only between frames of top hive body [ABJ, 6/04, p476].

Method #2 - Dissolve 35g of oxalic acid dehydrate in 1 liter 1:1 sugar syrup. Use 30ml for small colony, 40ml for medium colony, 50ml for a large colony (or 5 to 6 ml for each occupied super). Drip lukewarm solution directly onto bees between frames. Treat broodless colonies in Nov - Dec when ambient temperature is above 32oF. Use freshly prepared solution or solutions that have been stored for max. 6 months at max. of 59oF.[http:www.beedata.com/files/drip-oxalic-bogdanov.PDF (http://www.beedata.com/files/drip-oxalic-bogdanov.PDF), Bee Tidings, Jan 03, and http://www.stratford-upon-avon.freeserve.co.uk/PENotes/VarroaTreatment.htm].

Effectiveness - 89-97%117. >90% [ABJ, 6/04, p475]. An efficacy of 95% after 3 treatments using a 5% solution (w/o brood). With brood, 39.2% after 3 treatments [ABJ, 8/05, p672]. A European study seeking to optimize mite mortality rates and reduce adverse effects from oxalic acid in sugar syrup treatment showed 92.2% efficiency using 3.2% oxalic acid in 60% sugar syrup. 4.2% oxalic acid produced slightly better efficiency, but more adverse colony effects. 2.9ml of syrup / comb was more effective (92% mite kill) than 2.5ml / comb (80%)116.

Adverse Effects - Conflicting reports to OA effects on bees range from no deleterious effect to impaired queen performance and poor overwintering success [ABJ, 6/04, p479]. Trials suggest that some hives show adverse effects from DRIP treatment29.

Storage of prepared 1:1 sugar/water/OA solution - Sucrose solution used for trickling changes its color (to brown) after prolonged storage at room temperature as hydroxymethylfurfural (HMF) content increases. This is the substance used to detect a loss of quality in overheated honey. Sucrose solution w/ a high HMF content is toxic to bees. Use freshly prepared solution or solution can be stored a maximum of 6 months at a temperature of 59OF (15OC). Storage at or below 39OF (4OC) is ideal.

Treatment Cost -

3) SPRAY treatment is better tolerated by the bees. Use 3 - 4ml (3% concentration) per frame side. Mix 30g dehydrated OA in 1 liter of water [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/os_lagerung_e.pdf].
• Do NOT use during honey flow.
• Two autumn treatments are generally required.
• Labor for spray application has been estimated at 14 minutes per beehive50.

Effectiveness - 82-99%69; 114; 47.

Adverse Effect - Conflicting reports to OA effects on bees range from no deleterious effect to impaired queen performance and poor overwintering success [ABJ, 6/04, p479]. Long term (4) SPRAY applications of 3% oxalic acid in autumn and spring showed significantly negative effects on brood development and queen survival62, although other studies did not show such effects114; 19.

Treatment Cost -

4) PAPER TOWEL method called OsInAl (OxalSaure In Alcohol). OsInAl can be used in fall, even when colonies are breeding. You can leave the OsInAl tissue in the hive during the winter. OsInAl is NOT suitable to treat strongly infested colonies in summer. It is useful to treat splits with OsInAl. The bees must have contact with the tissue. OsInAl is not immediately effective like OA trickling. The effect lasts over several months.

Formula for 40 tissues: 200g oxalic acid, 1 liter 70-90% alcohol, 50g citric acid. You can use thin tissue (cheap towels for cleaning) made of PE-fibers or other artificial material in size of 20x25cm (about 8x10”). Dissolve the oxalic and the citric acid in the alcohol. Put the batch of towels in a plastic container and spill the solution over the towels. The alcohol is used to resolve the oxalic acid. The alcohol evaporates within 2-3 days and the OA is evenly spread in the towels. Pay close attention, alcohol kills the bees! Do not use the towels soaking wet! Citric acid (hygroscopic) is needed to (keep) towels wet in the hive. OsInAl works much better, when the towel is wet. Kills 60-90% of the mites.
[Bumble Bee, http://www.beesource.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=3;t=000316;p=2#0000 32 - Accessed 2/21/05].


OXAMITER STRIPS - (Ingredients: Different natural acids including oxalic acid and scented oil) A long-term treatment that should begin in spring or after harvest. Use 1 strip per 9 frames. Hang strips between brood frames or place across top bars. Strips should remain in hive for a period of 5 weeks, and should be replaced if removed (chewed up) by bees. At end of treatment period (5 wk), remove remnants and store securely in original package, closing bag w/ tape and place in a dark, dry location until next use.

Monitor after Treatment - Repeat if mite drop exceeds 20 or more mites at end of 5 weeks [http://www.members.shaw.ca/orioleln/new_oxamite.htm].

Source / Cost - $12.50 per 10 strips

OXAVARR - Kill some bees, but not enough to be significant. Available in Uruguay and Chile [BC, 1/05, p21].

COWEN VAPORIZER by Cowen Manufacturing Co. Inc., Parowan, UT. Available 2005 [BC, 10/05, p6].

HEILYSERR VAPORIZER - Heilyser Technology Ltd., 685 Dalkeith Ave. Sidney BC, V8L 5G7
• Model JB200 is powered by 12-volt car battery. COST - $65.00
• Model JB600 is for use w/ Styrofoam Hives. COST - $49.00
• Model JB700 requires a propane torch. COST - $67.00
• Model JB700D can treat 2 colonies at same time. COST - $168.00

VARROXR VAPORIZER - German made (Mellifera e.V.), distributed by Andermatt BIOCONTROL AG, Stahlermatten 6, CH-6146 Grossdietwil, Switzerland. World-wide patent pending.
• VX100 Vaporiser is powered by 12-volt car battery. COST - About $148.00 (120,00 Euro)
• VX101 Extension Cord, 7m. COST - About $47.00 (38,00 Euro)
• VX102 Mask (FFP 3 S/L) COST -
• VX200 Oxalic Acid Tablets, 100ea. Available soon in blister packs.
COST - About $25.00 (20,00 Euro)
[http://www.imkerei-technik.de/varrox_verdampfer.htm - Accessed 7/13/04].
• Hive entrance must be minimum of 0.409” (14mm) high and 3.169” (85mm) wide to introduce the VARROX vaporiser [http://www.mellifera.de/engl2.htm-Accessed 2/3/05].
• Uses 2 g OA dehydrate per 3 minute treatment.
• Effectiveness - 97% [http:www.imkerei-technik.de/varrox_verdampfer.htm (http://www.imkerei-technik.de/varrox_verdampfer.htm) - Accessed 7/13/04].
96.8% (92-98%) [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
95% for single treatment [http://www.mellifera.de/engl2.htm-Accessed 2/05].

VARREXR EVAPORATOR - Consist of a heatable pan filled w/ oxalic acid dehydrate and connected by cable to a 12 volt car battery. Pan is pushed through hive entrance underneath brood combs. Similar to VarroxR Vaporizer [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Uses 2 g OA per 4 minute treatment [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Effectiveness - 90% (76-96%) [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].

ISENRINGR EVAPORATOR - A bent copper tube sealed at lower end. OC is filled into tube and tapped downward. Tube is inserted through hive entrance underneath brood combs. Lower part of tube containing OC is heated outside hive using a flame
• Uses 3 g OA per 3 minute treatment [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Effectiveness 88.6% (38%-96%) [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].

VARROGAZR EVAPORATOR - A vertical copper tube is filled w/ OA and heated w/ a flame, and a horizontal copper tube is inserted into hive. A small 1.5 v battery-powered ventilator is fixed to horizontal tube and blows sublimated OC into hive [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Uses 2.4 g of OA per 3 minute treatment [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Effectiveness - 92% (89-98%) [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].

KRUSOR EVAPORATOR - A special gas burner is connected directly to evaporator and sublimated OA is introduced into hive by means of a plastic tube inserted through entrance [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Uses 2.4 g OA per 3 minute treatment [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].
• Effectiveness - 29% (15-42%) Unsatisfactory treatment success is due to sublimated OA re-sublimates within plastic tube due to low temperature. Only a small part of OA reaches colony in form of an aerosol [http://www.apis.admin.ch/en/krankheiten/docs/saeuren/osverdampfen_e.pdf].

REFERENCE: (Except as noted)
Review of Treatment Options for Control of Varroa in New Zealand. Dated Feb 2001. http://www.maf.govt.nz/biosecurity/pest-diseases/animals/varroa/papers/varroa-treatment-options.htm – Accessed 2/27/04.

03-06-2006, 04:44 PM
"OA is a naturally occurring component of our nourishment. It can be found in almost every plant we eat and is a natural component of honey (0.02 to 2 g/kg). Rhubarb becomes sour because of 2.6 to 6.2 grams of OA that is contained in each kilogram of fresh plant [http://www.mellifera.de/Engli2.pdf]."

There's been a number of comments relating that oxalic acid occurs naturally in rhubarb leaves and other plants. This is of course true but misleading as raw rhubarb leaves have caused illness and even death in many people who have eaten them in quantity. Thats why we cook rhubarb and avoid the leaves. Natural is not the same as harmless.

Ben Brewcat
03-06-2006, 04:52 PM
Holy cow Dave, thanks for all the info! Do you have an alternate source/address for the http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/guidelines/control.htm re: not using while honey supers are on? Seems like I've heard it's OK while human honey is being collected.

Informative thread even by Beesource standards!

03-06-2006, 04:57 PM
Dave............ Wow

George Fergusson
03-06-2006, 06:01 PM
Yah, Dave W is all over the record keeping thing. Good thing, somebody has to do it.

Good job Dave smile.gif

03-06-2006, 06:06 PM
Holly crap Dave. I think you just about covered every single question and thought I had about Oxalic Acid. Thanks for your time!!

I am using your post for future references!!

I dont know if I agree with the OA exposure to people cutting rhubarb. Seems your talking a huge dose,
My grandmother has always told me to never eat rhubarb leaves, for it will make me seriously ill.

03-06-2006, 11:20 PM
This is just a suggestion. When using OA vapors you need to vent the hive after the usage. I wait 15 min them pop the cover to vent. Also the build up is from too much used on the colony.The amount to use for every 2 deeps is 2 teaspoons. I have used it for 6 years and never had a build up problem. Also treatment need to be done 45 days before honey supers can be put on. Just a thought.

Dave W
03-07-2006, 08:29 AM
Ben Brewcat . . .

>Seems like I've heard . . .
I've "heard" a lot of things too, but do NOT have a source to confirm "OK while human honey is being collected".

Please, if you find a source, let me know, I would like to make myself a note smile.gif

03-07-2006, 10:12 AM
Hi Dave,

That's quite a compilation! The http://www.geocities.com/usbwrangler/oxal.htm link is no longer valid. Yahoo unilaterally canceled my usbwrangler id. And that site was lost.

The info is now at:

The 'crack pipes' worked great for my very limited need for treatments. But I would suggest that the commercial guys check out oxalic dribbling. That's what most of my commercial friends are using now. The solution is applied to the active part of the hive. That should keep any residues in those less accessible areas to a minimum. And thus limit a beekeepers exposure.


03-07-2006, 10:20 AM

……….The amount to use for every 2 deeps is 2 teaspoons….

I never heard this before and I would say it is 4 times the amount you need.

IMO the right amount OA in an evaporator is 2 - 3 grams or ½ tee spoon per treatment.
You can’t do more than kill the mites.

The hive has to be closed for approx 15 minutes after the evaporation. During this time the OA vapour comes in contact with moisture and humidity in the hive and converted in microscopic fine acid drops.
As soon as Varroa come in contact with is this liquid acid kills them.

………..I wait 15 min them pop the cover to vent……..

I only open the entrance after 10 – 15 minutes. There is no acid smoke left bees can blow out.
When OA evaporates the fog settles down on everything in a short time. If you don’t believe it try an evaporator with a metal pipe. As soon as the pipe is to long oxalic acid block them in a short time.

……..Also treatment need to be done 45 days before honey supers can be put on…..

Has anyone heard about this (45 days) or where can I find references?

Dave W
03-08-2006, 08:31 AM
B Wrangler . . .

>The http://www.geocities.com/usbwrangler/oxal.htm link is no longer valid.
>The info is now at:

Thanx, Ill make note smile.gif

03-08-2006, 08:55 AM
>Seems like I've heard it's OK while human honey is being collected"

as for OA with honey supers on, or any other method that may cause some honey contamination with OA, you must consider this:

Some people must avoid foods that contain tiny amounts of Oxalic Acid. It can make them sick. I have a friend with a condition that requires this. What if your honey has some OA in it, then one of these people eat your honey?

Any chemical treatments in a hive while honey supers are on, is a setup for serious problems. If you're doing your job there will be no need to treat with honey supers on, or close to on.

03-08-2006, 10:29 AM

………….What if your honey has some OA in it, then one of these people eat your honey?……..

OA is a natural ingredient in honey even without treatments against Varroa mites. The amount is different, depends what kind of flowers the nectar comes from.

Almost all plants contain more or less (small amounts) OA, to prevent any kind of OA in your body… stop eating. http://www.mellifera.de/engl2.htm

I like to eat my own honey therefore I would never treat with honey supers on. That’s also the reason why I not go for Perizin (chumafos) or any other chemicals. OA doesn’t contaminate wax or sealed honey.

…………Any chemical treatments in a hive while honey supers are on, is a setup for serious problems. If you're doing your job there will be no need to treat with honey supers on, or close to on…….

I agree with you, but chemicals contaminate the wax and honey beside the brood nest. As soon as a honey super comes on bees transport the contaminated honey up to get more space for brood.

Treat with Perizin – Checkmite, or others, for 40 some days you can find the chemicals the next years in wax and therefore in honey. It might be only ppb but it is detectible.

03-08-2006, 12:34 PM
agree with what you are saying Axtmann, also aware of its presence in many foods.

Possibly honey is one of the foods my friend is not supposed to eat, I don't know.

Putting OA in the hive with honey supers on will surely raise the level to "unusual" at the least. Then, if someone like her develops a problem from it the beekeeper is responsible for that.

I'm all for using OA as long as we educate ourselves on its proper, safe use.

I used Thymol last fall and read up on the organic acids at that time. I've only done fall treatments in the past, but may buy some succrocide to do emergency treatments in spring. I had thought about using OA in spring for emergencies, but I don't want to do it just before supering. I like to allow a good amount of time for affected honey to be consumed and residues to dissipate and degrade for any organic chemical use.

Its good to hear input from you and others in Europe where actual research on OA and Thymol has been done; resulting in approved use. USA is way behind in this as you know.

[ March 08, 2006, 01:34 PM: Message edited by: MichaelW ]

Bob Harrison
03-08-2006, 02:13 PM
A study at the institute of occupational and social medicene found:

"There is no risk to the health of the apiarist"

Research going on in the U.S. reported at the ABF convention (2006 Louisville) that with use of a mask the apiarist is fairly safe. Without a mask a health risk exists.

03-08-2006, 06:13 PM
>>A study at the institute of occupational and social medicene found:

>>"There is no risk to the health of the apiarist"

Are they extending the risk assesment further to acknoledge the potential risk that evaporated dust after the treatment has on the beekeeper.

Many here say its very low, but as mentioned earlier here > low exposure over thousands of hives with multiple treatments a year, over years of treatments has to be considered into the beekeepers risk assesment.

Bob Harrison
03-08-2006, 08:00 PM
Dr. Marion Ellis was the presentor at ABF. He has been working with OA for two years in Nebraska I believe.
I only post to caution those using OA that a respirator is a small safegaurd for ones health.
I live on a farm and also run a small orchard.
I have buried two close friends which developed cancer. Both refused to wear a respirator while spraying their orchard.
You lining of your throat & lungs are very susceptable to chemicals.
I am not saying not to use OA but only that I disagree that OA use is safe without caution.

10-19-2009, 10:00 AM
Thats funny, my dad has been using oxalic acid for 25 years, I guess he hasnt ever got any on his hands because he is very healthy