Oxalic Acid Dribbling

The Idea

Varroa mite. Photo courtesy of Scott Bauer of the ARS.

Dribbling oxalic is a non-contaminating, relatively safe, and cost effect varroa mite treatment. It is quick to apply and can be used when hives can be opened.

The Details

Why Dribble It?

It’s a safer way to get oxalic into a hive when the conditions are right.

  • no fire danger
  • no errant fumes

Formulation Basics

Accuracy is required. For some reason, oxalic acid solutions are much harder on the bees than are the oxalic fumes. It’s imperative to get the concentrations right. And to apply them correctly or the bees will suffer for it.

A good scale is required to accurately prepare the oxalic solution. I purchased one from Americanweigh. And was pleased with their selection, price, and service.

European Formula

The Europeans have decades more experience dribbling oxalic acid than anyone else.

They recommend preparing a basic 1:1 sugar solution by dissolving 1 kilogram of sugar in 1 liter of warm water resulting in 1.66 liters of sugar syrup. Then stir 75 grams of oxalic acid into the sugar syrup until dissolved, yielding a 3.5% oxalic solution.

Canadian Formula

The Canadians have done more formal recent research and have approved it for use. Be sure to read the Canadian label before dribbling. It states the formulation and the safety requirements.

They recommend 35 grams in a liter of 1:1 sugar syrup by weight or volume.

Formula Differences

A difference exists between concentrations in the two recommended formulas after adjusting for the differing volumes. It appears this difference results from the different molecular weight of oxalic acid and oxalic dihydrate, the most commonly available form.

Allen Dick has a webpage discussing these differences.

Be sure to check which kind of oxalic you have and adjust your formulation.

Application

How to do it

  • read the Canadian label
  • use the appropriate safety gear
  • dribble 5mls of acid solution between each set of frames completely occupied by bees
  • put the solution right on the bees
  • use less for partly occupied frames
  • don’t put more than 50ml of solution in one colony
  • don’t treat more than once a season if bee flight is restricted

When to do it

Dribbling works best when the hives are broodless.

Reports show two treatments, one late fall and another early spring, are OK if the bees can fly.

Contraptions

Beekeepers are an inventive bunch. And equipment abounds for getting the oxalic solution into a hive.

A beekeeper with a few hives is at an advantage. He can take his time. Individually evaluate a hive. And use simple equipment to safely and accurately apply the correct dose. A simple plastic bottle, marked in 5ml increments, is all that’s needed. Or an appropriately sized veterinary syringe would work as well.

Automatic syringes , homemade sprayers, etc. are commonly used by beekeepers with many hives to treat. Problems abound with most of this equipment.

  • oxalic acid corrodes seals
  • solution under pressure can erratically spray or leak
  • it’s hard maintain an accurate dose with changing pressures or temperatures
  • multiple head sprayers treat all hives the same regardless of bee population

I suspect that the problems experienced by some commercial beekeepers while dribbling oxalic result from improper application.

Have your own design? Just be sure safety and accuracy are at the top of your design criteria.

Storage

The oxalic solution has about a two week shelf life at room temperature. If it turns color or is older, mix up another batch.

Any excess solution can be refrigerated or frozen almost indefinitely. But it’s probably best to get rid of it. The risk that someone might inadvertently get poisoned with it while it’s stored in the refrigerator, far outweighs any cost savings. Were talking tenths of pennies per hive here!

-bwguy

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