Comparing Two Ways to Use Oxalic Acid in Bee Colonies

Oxalic acid application for varroa mite treatment is generally done in late fall or winter because there is less capped brood in the hive. Occasionally, summer application is acceptable, but only when supers are not in place. There are two ways to introduce the oxalic acid into the hive: squirting a mixture of oxalic acid and sugar syrup on the bees between the frames (oxalic acid dribble) and inserting a device into the colony and heating it until the oxalic acid in the pan burns off (oxalic acid vaporization).

There are two ways to introduce the oxalic acid into the hive: squirting a mixture of oxalic acid and sugar syrup on the bees between the frames (oxalic acid dribble) and inserting a device into the colony and heating it until the oxalic acid in the pan burns off (oxalic acid vaporization.)

Both the oxalic acid dribble and vaporization methods:

• Are effective ways to kill varroa mites in their phoretic state.
• Use oxalic acid dihydrate as the active ingredient, and both use about the same amount per hive, so the material cost is equal.
• Require that the operator take safety precautions to protect themselves while applying the oxalic acid.

While there are similarities between the two methods, there are also important differences between them.

The main difference is in how the oxalic acid is delivered to the hive. The oxalic acid dribble method uses simpler equipment, but it is considered to be slightly harder on the bees, limiting the ability to treat again, if needed. The other method, oxalic acid vaporization, uses more complex equipment, and requires additional protective gear to protect the operator’s health. But paradoxically, it is less harmful to the bees so it offers more flexibility to repeat a treatment when warranted.

What is an oxalic acid dribble?

An oxalic acid dribble needs inexpensive equipment to prepare and dispense a mixture of oxalic acid and sugar syrup. The operator safety risks with this method are lower than with vaporization, so only a simple particulate (N-95) mask, eye protection and gloves are required as personal protection equipment. But it is somewhat harder on the bees because they will inevitably eat some of the sugar syrup, and in doing so, also consume some oxalic acid which is mildly harmful to them.

As an early winter treatment, it requires opening the colony in cold weather and breaking the boxes’ propolis seals at a time of year when the bees may not have warm-enough temperatures to repair the seals right away, potentially exposing them to cold drafts. It wets the bees during cold weather. Oxalic acid dribble should only be done once on the same cohort of bees.

Still, it may be a good place to try out a broodless-period, one-dose, oxalic acid treatment program.

» Read more about how to do an oxalic acid dribble treatment

What is an oxalic acid vaporization?

Oxalic acid vaporization requires a specialized tool (a Varrox wand or a ProVap device), a power source (typically a lawn mower battery), breathing protection (for a Varrox wand use a half-face respirator with acid gas cartridges, a ProVap requires a full-face respirator) and goggles. Vaporization is easier on the bees than a dribble. In fact, it has an excellent safety record and is considered to be harmless to bees, brood, and queens. It doesn’t require breaking apart the hive to apply. It can be used in a series of treatments, when needed. In the long run, compared to a dribble, many people consider vaporization the better choice.

There is one caveat: vaporization is best used only in wooden hives, not ones made of synthetic materials such as the BeeMax or Lyson equipment.

The principal barriers to using vaporization are the up-front equipment costs and the need to use a respirator while doing the treatment. Oxalic acid vaporization is very safe for the bees and highly effective against mites. However, because of the operator safety risks, if you cannot commit to always wearing your respirator, then vaporization is not the right treatment choice for you. Good control of varroa mites is important, but not at the cost of human health.

What kind of respirator is needed for oxalic acid vaporization?

There are several good brands available. For the Varrox wand, you want a half-face respirator with acid gas cartridges. (For the ProVap, you’ll need a full-face respirator with the same cartridges.) The right cartridge will have a yellow band around the perimeter. Acid gas cartridges are sometimes combined with organic vapor protection, and that’s fine. But you don’t want stand-alone organic vapor cartridges, even though they are commonly available. The half-face mask that we sell has the right ones. If you already have a respirator, you can usually purchase replacement acid gas cartridges to complete the set. And don’t forget: unless you are wearing a full-face mask, you also need to wear goggles to protect your eyes.

Be sure to study the User Instructions that come with your mask to learn how to do a proper seal test. Doing the seal check only takes a few seconds. And then repeat the seal check every time you put on the mask, even if you only had it off for few seconds.

» Read more about how to do an oxalic acid vaporization treatment