varroa mites

Oxalic acid approved for Varroa mites


The United States Environmental Protection Agency has approved the use of oxalic acid for use in honey bee colonies. According to information in the registration decision, “Due to the significant problems this parasite poses for honey bees, the EPA review of the application was conducted under a greatly expedited process.” You can read the full decision here, “Registration Decision for the New Active Ingredient Oxalic Acid.”

Contrary to the title, there is nothing new about oxalic acid for Varroa control. It is currently registered and widely used in Europe and Canada, and many U.S. beekeepers have been using it for years. Oxalic acid is readily available from hardware and paint stores where it is sold as “wood bleach.”

However, with the new regulation, its use will be legal and it will be labeled for use on colonies. The proposed two-page label can be seen here. It allows for the chemical to be administered in syrup, as a vapor, or as a spray.

Oxalic acid does not kill Varroa within capped cells and may, in fact, harm open larvae. As a result, oxalic acid treatments are most effective when brood rearing is at a low point. As with all miticides, the use of oxalic acid should be alternated with other preparations to reduce the chance of resistance.

In an upcoming post, I will share my system for using oxalic acid in a beehive.



Oxalic acid. © Rusty Burlew


  • Great News!!! I submitted comments in favor a month ago. I just got my vaporizer in the mail. I look forward to you sharing your system of using oxalic acid. I curious to know the brand and percentage pure you use as at our last bee meeting members were saying you need to be careful as some oxalic acid out in the market contains a high concentration heavy metals.

  • I just removed a hive of bees from a 5 gallon plastic bucket and they have been there for some time. The number of bees are about 25 to 30 thousand. Problem there was not any brood (none) and could not find a queen. The hive contained honey, pollen and plenty of comb some of which is old comb. Any suggestions of what is happening?

  • Rusty,

    As you say oxalic acid is very widely used in the UK, usually mixed in a syrup and trickled onto the bees in late December or early January when they are broodless. It is highly effective in killing the phoretic mites, around 90% according to our official sources (FERA – Food and Environment Research Agency). If applied by sublimation, it can be up to 97% effective, according to recent research at Sussex University which you can see at


  • So, where would we buy this? By the way, I am thrilled to say that my little free non-paying renters, are doing great! and thriving! The beehive is buzzing! I think I need to add another box pretty soon!

    Rusty, do you have any suggestion in how to deal with beetles? There are all over the place in my beehive. I got a suggestion from Brushy Mountain Bee Farm to put down a plastic mat (like the ones used in the offices). I have a real problem with this things; I even find ear wings in the hive!

    Any suggestions in how to deal with these 2 bugs; will be greatly appreciated!

    Howdy yall LOL from Friendswood, TX

  • Looking forward to your upcoming post on this method. Entering my third spring with the bees I find myself more than ever thirsty for knowledge. You have become my go-to-source for many of the issues that beekeepers are facing. As I have said before thank you so much for your efforts with this blog. Every time I hear about a subject or a new technique I search it out on your posts. Your ability to shred right through all the “hoopla” and get down to the issue at hand is a rare quality and much appreciated.

    • David,

      Thanks for you kind compliment! Thing is, though, I learn equally as much from all the people who write in and tell me I’m crazy or who suggest a better way. It’s definitely a two-way street.

  • I am failing to see how good WOOD BLEACH will be for the honey bees. I think that I will stick to using my EO’s …

    • Sheri,

      True, the organic acids are hard on bees, however they are not as devastating as the mites. Sometimes we have to make choices between evils. Remember, too, that oxalic acid is not the only organic acid used as varroa control: hop beta acids and formic acid are other examples.

      Put in perspective, oxalic acid is a regular part of the human diet, found in vegetables such as rhubarb, swiss chard, beet tops, spinach, and sorrel. Yes, it is toxic when concentrated, but so are your essential oils. In fact a popular essential oil for varroa mites is wintergreen, which is toxic to mites, bees, and humans when the concentrations are great.

      The adage, “the dose makes the poison” is true. Used in lesser concentrations, these preparations are usually harmless to bees but equally harmless to varroa. That is why timing, concentration, and strict adherence to directions is so important.

      Oxalic acid is a normal component of honey, and its use in the hive apparently does not increase the amount found in cured honey. Thus, it’s a better choice than using a product that is not a naturally-occurring component of honey.

  • I live in Denmark and we are also using oxalic acid every winter. I know that in Italy they are begining to use it in the summer. They trap the queen in a small cage inside the hive. 28 days later they drip syrup with oxalic acid in broodless hive.

  • Rusty,
    As per your request for questions to be attached to blog posts, I have a question relating to estimating mite loads in a hive. To your knowledge, is there a formula, or can you direct me to a reference that would help me estimate the total mite load in a hive from the result of either a 48 hour sticky board drop or a sugar shake?

    I have used a sugar shake for some time now as a threshold for determining treatment level. In an independent study I’m just embarking on, it would be useful to know what the total mite load might be in a given hive.

    I realize that any result would rely on a qualitative evaluation on my part as per hive strength, sample quality and any number of other conditions. Any help would be greatly appreciated.

    • Bruinnie,

      This is from the University of Minnesota: “If you know how many bees were in your sample, you can estimate the number of mites per 100 bees. If there is brood in the colony when you sample, you should double this number to factor in the amount of mites in worker brood. For example, if there are 5 mites/100 bees, the total infestation is probably 10 mites/100 bees. If your colony has over 10-12 mites/100 bees, you should consider treatment.”

  • Hi Rusty, I am getting confused as to the difference between oxalic acid dihydrate and oxalic acid crystals. I am reading oxalic acid crystal is actually a much stronger product than oxalic acid hidrate. Is that correct?

    • Melissa,

      The one that is labeled by the EPA for use in bee hives is oxalic acid dihydrate crystals (This is the one commonly found in wood bleach). The stronger one, often found in laboratories, is oxalic acid dehydrate. Note again, one is dihydrate and one is dehydrate. According to Randy Oliver, if you use dehydrate, you must use only 7/10ths as much as when using the dihydrate.

  • I treated my hive with Oxalic through vapor treatment- Now my bees have all left in Nov? Is the honey left behind (was to be used for the bees winter food) good to eat?

    • Charles,

      It should be fine to eat. Oxalic acid treatments don’t affect honey, and honey contains a certain amount of oxalic acid in any case. So unless you treated with other pesticides, I’m sure it will be fine. Of course, if you’re going to start another colony in spring, that stored honey is great for that purpose too.

  • Rusty,

    I forgot to mention that beekeeper, Les Crowder, mentions in his book about adding creosote/chaparral leaves to the smoker to help with preventing varroa here in NM. From that info, I wondered about adding herbs/vegetables with oxalic acid to the smoker.


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