Formula and Procedure for Making Oxalic Acid Cardboard Strips

[Gabriel Harber]

For those of you who are treating your bees, I have just completed my second round of Oxalic Acid cardboard strips.  I find MAQS to be unpleasant to work with and was looking for soft treatment that was fairly easy and inexpensive.  I plan on installing strips into a couple colonies with high mite counts this week. 

Before you start, please read the references below:

https://www.researchgate.net/publication/283489668_A_new_formulation_of_oxalic_acid_for_Varroa_destructor_control_applied_in_Apis_mellifera_colonies_in_the_presence_of_brood

http://scientificbeekeeping.com/beyond-taktic/

All the treatment discussions online are seemed to be geared toward deep brood boxes. I run mediums. 

The last time I made these strips, I used 2 parts glycerine to 1 part OA.  In an effort to increase the concentration of OA in each strip and use less glycerine, I tried a 1/1 solution of OA to Glycerine with my latest batch.  This is a very concentrated OA solution.  You will need to warm the solution and stir in order to get all the OA to dissolve in the glycerine. 

I cut standard cardboard sheetrock shims from Home Depot which measure 45” long into quarters.  This is much easier and more consistent than cutting strip from egg cartons or other salvaged material.  Each strip measures 11.25” and weighs about 8.5g dry.  You get 4 strips per shim with no waste.  For this round of strips, I dissolved 540g (all the OA I had) with 600g of glycerine (all the glycerine I had).  Next time I will try equal parts OA and glycerine for ease of accounting.

Use dedicated tools as solution is very acidic.  My stainless steel spoon started looking a little grey after 10 minutes of stirring.   Glycerine must be heated on low until all OA dissolves.  When you first mix the two it doesn’t seem like there is any way that the OA will dissolve in the glycerine.  Keep stirring on low heat.

600g glycerine - 36%

540g OA - 32%

510g cardboard - 31%

Total: 1650g

This batch produced 60 strips.

Once the OA has dissolved, pour over strips.  I used a rectangular plastic container with a lid.  I put the cardboard strips in the container, waited for the glycerine solution to cool, put on nitrile gloves, and poured the solution over the cardboard.  I then turned each strip a couple of times to make sure that all strips were getting wet.  I turned the each strip a couple of times before stacking them in groups of 15 or so and let them sit over night.  

In the morning almost all of the solution had been absorbed by the strips.  The cardboard is fairly delicate, so handle with care (try to not bend them until you install them in your hives).  The OA in the solution had begun to solidify out where the cardboard had not absorbed it, though there was very little solution left over.  

I stacked groups of 20 strips and weighed them.  Group 1 weighed 533g, group 2 weighed 536g, and group 3 538g.  For ease of accounting, I took the average and rounded up to the nearest whole number, which gave me 27g per strip.  27g times the percentage of OA should give the approximate concentration per strip- about 8.5g OA per strip.  The goal should be to get 8.5-10grams of OA per strip.

Given that the reference above suggested 40g OA per deep brood box, and I estimate a medium brood box to be 30% smaller, it seems reasonable that at least 28g of OA be applied to each medium brood box.  I will be trying 4 strips per brood box since I run mediums.

With the formula I just mixed:

3 strips-25.5g OA

4 strips- 34g OA

5 strips- 42.5g OA

Since drones have the longest gestational period at 24 days, it seems reasonable to leave the strips in place for at least 4 weeks.  During this period the bees will chew away the strips. They will typically chew mostly at the bottoms and at the contact points where the strip folds over the frames.  As with formic acid, and initial die off of diseased bees can be expected in the first few days after application.  The bees do not run from the strips as they do from MAQS and you don’t need to wear a respirator.  Wear nitrile gloves or other acid resistant gloves when handling the strips.

You can get 10lb of OA on Amazon for about $25 and 10lbs of glycerine on Amazon for about $25 as well.  A stack of 100 shims from Home Depot runs about $10 (for this volume of glycerin and OA, you would need to buy 2 bundles of shims).  

10lbs = about 4500 grams X2 = 9000g solution

You should be able to get at least 530 strips from 1 gal of glycerine, 10 lbs of OA, and 1.5 bundles of shims.  If you assume 8 strips per box, you should be able to get at least 66 treatments from the supplies above.  The cost per treatment would be about $.83 per.  

Ultimately, I think that using 10g of OA and 10g of glycerine per strip would be easiest.  That way for 100 strips you would be using 1kg of each.

Please feel free to follow up with questions, comments, and thoughts.

Gabriel

[nicole....@gmail.com]

Excellent write up! Thank you! It would be great if you could record mite counts before and after to see how effective different concentrations are and the effect that length of time in the hive has.

I've done similar trials with homemade formic acid pads that I use. It's interesting to see the different outcomes based on concentration and doseage intervals.

I've found that you need to keep treating until you get a zero or 1 mite count (I use sugar roll method). If you stop when counts are below 10 because you think that's good enough, then the mites rebound way too fast.