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Oxalic shop towel updates

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This page is for the sharing up updates on the OA/glycerin shop towel application method.  You can view a pdf of the article here: Beyond Taktic

I’m overloaded with emails regarding this subject.   PLEASE do not write me unless you have read the entire article, plus all the updates below.  Thank you for your consideration.

If you have previously viewed this page, please reload it to ensure that your computer is not showing you an outdated cached copy.  Only then, if after reading all the updates, you have questions or you’ve figured out ways to improve the method, please write me and I’ll post here.

I’m currently working with EPA to add this method as an approved application method (so that it can be used legally).

Update 14 Feb 2017

I’d had a number of people suggest rather complex manufacturing methods for spraying, vacuum suction, etc. methods for mass producing OA shop towels.  I appreciate your suggestions, but I will leave mass production methods to manufacturers.  What I’m focusing on are simple preparation methods for beekeepers.  My most recent formulation is at the 12 Feb update.

Some other recent questions:

Q:  I don’t remember reading how long you leave this treatment in place.

A: In the first place, this application method is not yet approved for use in the U.S.  You may be able to obtain an experimental use permit from your State department of pesticide regulation.  That said, the application method is designed for an extended release over a period of roughly one month, by which point the bees should have removed most of the shop towel.  Mite reduction is not immediate, and from my limited testing, appears to take about a month.  Therefore, if legal in your state or country, apply it as soon as the mite infestation rate (as determined by alcohol wash) exceeds 2 mites/100 bees.

Q: Can it be used with supers in place?

A: According to Maggi’s testing, this treatment does not appear to increase OA residues in honey.  I’m asking EPA to approve it for use with honey supers on.

Q: Does the ambient temperature matter?

A:  I’ve tested at up to 100°F (at low humidity), and did not observe any adverse effects.  I’ve also tested during our California winter (for adverse effects only–not efficacy), during sustained cold rain and some freezing temperatures.  Again, I observed no adverse effects upon the bees or brood.

Q: When sourcing your Oxalic acid/Glycerin etc have you looked at different grades of OA? I see you have food grade gly. I have been sifting through OA msds sheets from what we have locally available and the chemical composition varies wildly from agricultural bore cleaner or wood bleach to technical grade OA with prices that vary even more.  The lower end “bore cleaner” OA Dihydrate has Sulphate at 1000ppm and some metal elements included, Iron at 100ppm and Lead at 50ppm.

A:  The EPA requires registered “Distributors” of OA for varroa treatment to certify the purity of the OA.  Currently, Brushy Mountain is the only registered distributor.  I’m working with another registrant to bring prepared towels to market at an inexpensive cost.

Update 12 Feb 2017

I checked several hives yesterday that have had a OA/gly towel in them for the past two months during rainy, cold spring buildup.  There does not appear to be any adverse effect upon the colony.

Please remember that this formulation is not yet approved for use in the U.S. (I am in the process of obtaining an Experimental Use Permit for the State of California).  It is against the law to apply OA to hives in an unapproved manner.  I’m working with EPA and ARS to get this application method added to the label, but it’s a slow process.

Meanmwhile, I’ve been doing lots of kitchen chemistry to figure out how to avoid the need to press the excess OA/glycerin out of the shop towels in order to obtain a texture that the bees will remove.  It appears the total glycerin should not exceed 13 mL per towel.  This amount of glycerin will hold 12 g of OA, without the OA coming out of solution at hive temp.

I think that I’ve finally hit upon a formula that works.  It is difficult to get the solution to wick by capillary action into the full length of a roll of shop towels.  (For non U.S. readers, the Scott shop towels are a cellulose heavy-duty, highly absorbent towel http://www.kcprofessional.com/products/wipers/general/scott-shop-towels).

So here’s a step-by-step process that appears to make the ideal towel, although I need to confirm for efficacy in the hive.


Step 1.  Use a sharp kitchen knife to cut the roll of towels exactly in half crosswise.


Step 2.  Find a stainless steel saucepan that just fits the roll (stood on end).  The optimal formula appears to be (per towel) 12 g of OA dihydrate, 13 mL of glycerine, and 5 mL of water.  Multiplied by 55 towels + the cardboard roll = 56/2, for final amounts per half roll of towels of:

OA 336 g
glycerin 364 mL
water 140 mL

Yes, adding water turned out to be OK, so long as I use slightly more glycerin in mL than OA in grams.  The water will mostly evaporate from the towels, depending upon temp and humidity.  I show a graduated cylinder above on the right (most accurate), and a measuring cup on the left.P1210353

Weigh out the 336 g of OA (I actually use a more accurate beam balance, but it’s not critical).


You can preheat the water and glycerin in the microwave, or on the stove.  It doesn’t appear to be critical when you add the water, but if you add it first to the glycerin before adding the OA, it may help to prevent the formation of oxalic esters during the heating.


Heat to 140-160°F.  Higher temps will cause degradation of the OA and accelerate ester formation (both of which we wish to avoid).


Add the OA crystals, and use a stainless steel spoon (it may discolor) to stir while you dissolve the OA.  Wear nitrile gloves and safety glasses!  Keep the burner on the mixture while stirring, but do not allow the temp to exceed 160F.  With a modicum of caution, this is safe to do.


As soon as the mixture is completely clarified, remove it from the heat and place the pan on a plastic tray.


Preheat the roll of dry towels for 1 minute in the microwave–this preheating helps the solution to wick into the roll.  Although you can insert a piece of 1-1/4″ PVC pipe into the roll, I find no benefit from doing so, since the cardboard cylinder will come loose anyway.  Also no benefit to leaving the wrapper around the roll, since I get better absorption if the roll is allowed to expand.


Carefully place the roll into the hot solution.  The pan should first be placed on a plastic tray (not as shown).  The solution will quickly wick up part way.  When it gets to about 1/3rd of the way up, then flip the roll.


Use kitchen tongs to flip the roll.  The mixture will not immediately irritate your skin, and can be easily washed off with warm water. But it is sticky, and will get on all surfaces if you’re not careful.  It is really important not to allow traces of the solution to get on surfaces, as it is slowly corrosive, and a hazard.  You don’t want it ending up in your eyes!  Keep warm water and a wet sponge on hand for wiping surfaces.  A little bit of baking soda dissolved in water will immediately neutralize any acid.


The solution will wick up from the other end.


You may find it to be of benefit to flip the roll again.  The roll will absorb every last drop of solution.  Allow the roll to cool, and for the water to evaporate off (I’m not sure that this is necessary, as it would also occur later in the hive).  You can then place the roll into a secure plastic container or ziplock bag for storage.

I found that when I held towels in the solution at 150F for a few days (with or without water), that the acid dissolved the towel.  I don’t observe this happening at room temp, but have not had time to test to determine how long the treated towels can be stored before losing strength.  The Aluen CAP strips claim to be good for an extended storage period.  I will be performing tests to see whether the OA or towels degrade with extended storage.  For now, probably best to make them up fresh.

One would then apply two half sheets of towel per hive for a treatment, which would apply 12 g of OA to the hive.

I’m not completely sold on the rolled towels, and have the folded version on order, which I will test when they arrive.

I’m buried in email from those wanting more info.  Please only email me if you have something important to offer, or a serious question.  If you are not comfortable with accurate weighing, measuring, and safe handling of acids, YOU SHOULD NOT ATTEMPT TO DO THIS!

I am encouraging one cooperating bee supply company to bring an inexpensive premade version to market.

Update 24 Jan 2017

There has been lots of response to my article on OA/gly in ABJ.  I’m in communication with EPA to get this application method approved.

I’m in the middle of a trial of OA/gly shop towels on 6 hives during our wet, cold winter.  As of today, after ~3 weeks, the colonies are not showing any adverse effects upon the bees.

I’m currently working on is the best ratio of OA to glycerin, and the best amount per towel.  The problem is that the towels don’t want to evenly absorb the optimum amount of glycerin to leave them less “oily” so that the bees will chew at the towels.  I’m trying to figure out how to get a full roll of towels to absorb the right amount of solution without the need for squeezing out the excess.

I tried 700g OA in 700ml of glycerin, heated to 160F, and the roll of towels preheated 1.5 minutes in the microwave.  I poured the hot solution into a tall, narrow asparagus pot, and set one end of the towel roll into the pot.  When the solution had soaked half way up, I flipped the roll over, and placed the roll into a warm oven.  After 15 minutes, the solution has still not absorbed to the center of the roll.  So I left it for another hour in the warm oven.  This proved to be a mistake, since the acid degraded the lower part of the roll into a soft mess.

The 700ml of glycerin also appeared to be too much–leaving the towels too “oily” feeling.

I’m now going to experiment with adding isopropyl alcohol (boiling point 180F) to the solution, and decreasing the amount of glycerin.


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