Maine State Apiarist Announces Oxalic Acid Registration in Maine for Treatment Against Varroa Mites

As additional follow up on oxalic acid (OA) discussions at the January 2016 Androscoggin Beekeepers Club (ABC) meeting, ABC VP contacted Maine State Apiarist Tony Jadzak for the official word on both the registration of oxalic acid in Maine for use against Varroa destructor in honey bee hives and recommended methods of OA treatment.

In response, Tony provided the ABC with a copy of a document he prepared titled “Oxalic Acid Registered for Varroa Control“.  This document had already been provided to the Maine State Beekeeper’s Association (MSBA).

A PDF version of the original Microsoft Word document Tony provided is available here.  For the convenience of ABC members and interested individuals, we’ve reproduced the text of Tony’s document below.

Note that Tony concludes his description with the words: “Please read and follow the label.  Remember, ‘The label is the law’.”  Tony was also kind enough to send a PDF copy of the label and you can access it from the following link:

EPA label for Oxalic Acid Dihydrate (number 91266-1-91832)


Oxalic Acid Registered for Varroa Control by Tony Jadczak

The toxicity of oxalic acid (OA) to Varroa has been known for nearly three decades based on experiments conducted in Asia and later in Europe.  The initial tests compared spraying weak OA solutions on bees, trickling OA sugar syrups into honey bee colonies  and OA fumigation (vaporization).  All of these methods demonstrated very high efficacy and were quickly adopted by beekeepers.

Early use of OA by European beekeepers involved spraying each comb of bees in broodless colonies with a 2%- 3% OA water solution.  The technique was effective but time consuming since each comb covered with bees had to removed and sprayed on both sides for control.  The treatment was later modified to make the application more efficient by adding the OA into sugar syrup and “trickling” 5-6 ml on the bees clustered between combs.  The role of sugar is unclear since minimal OA syrup is consumed by the bees and mite mortality is from contact with the acid.  It is thought that the sugar solution adheres to bees better or the sucrose makes the solution more hygroscopic

During the 1990’s European bee researchers tested the effects of different OA concentrations and syrup solutions on both the mite and bees via the trickle method.  Researchers found optimal Varroa control at OA concentrations between 2.1% and 4.2% with concentrations of 2.8% and 3.5% the best regarding mite mortality and minimal damage to bees.  Researchers also compared Varroa mortality in OA treated hives when brood was present vs. absent.  Varroa mortality in hives with brood was 25% and 39.2% at the 2.9% and 4.2% OA concentrations and 97% and 99.4% respectively under broodless conditions.  Experiments indicate that increasing the dosage of OA above 3.5% does not improve efficacy and high doses of OA aren’t used due to bee toxicity.  Research clearly demonstrates that OA is most effective in broodless colonies for both the trickle and fumigation techniques.  The application of OA via trickle or vaporization in late fall/early winter affords beekeepers and excellent varroa “cleanup” for colonies with residual mite populations that rebound after late summer varroa treatments and/or hives that become reinfested by robbing hives undergoing varroa collapse.

As is the case with other registered Varroa controls, researchers have also identified issues related to the OA trickle treatment.  For example: 1-When brood is present repeated applications of OA can result in higher queen and adult bee mortality and a reduction in the amount of brood that can last for two months.  2- The midguts of honey bees fed OA sugar syrup have an elevated level of cell death but under field conditions bees tend to avoid consuming syrup with OA. (This may explain why a recent report stated that bees treated with OA have a lower nosema incidence.)  3- In some instances bees show poor tolerance to OA trickle applications.  Colonies receiving an overdose (excessive amounts, short –term repeated applications or excessive concentrations) can be weak in spring or die during winter.  Some studies have found that certain colonies do not tolerate the OA trickle even at normal doses.  4- Low temperatures can diminish the efficacy of OA treatment. 5- There may be a correlation with increased bee mortality when applied during periods of high humidity.  Further research regarding high environmental humidity is needed.  6- Prolonged storage of OA syrup solutions result in a change of color to brown.  Analysis indicates a high increase in hydroxymethylfurfural (HMF) that may be toxic to the bees if ingested. As a precaution, it is recommended that beekeepers administer freshly prepared solutions of OA syrup or use premixed solutions that are stored in the refrigerator.  Solutions can be stored for a maximum of 6 months at a storage temperature of 59 degrees.

Following are European recommendations and remarks for OA trickle treatment or the “Solution Method” as it is called on the US EPA label.  Some of these recommendations appear on the US Oxalic Acid Dihydrate label.

·         Trickle 5ml of OA solution directly on the bees clustered between the frames (occupied bee space) in each hive body.

·         The maximum dose of OA solution is 50ml. (i.e. 30ml for a small colony, 40ml for a medium-sized colony, and 50ml for a large colony.

·         Use only in late fall or early spring when little or no brood is present.  The European recommendation: carry out one treatment in broodless hives only in autumn (Nov.-Dec.).

·         Treat with lukewarm solution.

·         Apply treatment at an outdoor temperature above freezing (32 degrees).

·         Use only freshly made-up solutions or those stored for no more than 6 months at a maximum of 59 degrees.

·         Do not use when honey supers are in place.

·         Apply only when monitoring indicates treatment is required.

·         Wear gloves, safety goggles and respiratory protection during treatment.

There is much less published literature regarding OA heat vaporization (sublimation) in comparison to the OA trickle method.  Research and reports from beekeepers indicate that the vaporization technique does have some advantages.  Research suggests it is less detrimental to adult bees, brood and hive strength following application and from the beekeeper’s perspective, there is no need to unwrap, open hives and disturb the cluster during winter.   The risk to the applicator, however, is somewhat greater due to the potential of inhalation of the OA fumes.

European research indicates that when brood is present, vaporization 3-4 times at weekly intervals in spring is an effective Varroa control. However, the US OA label does not address this strategy and European recommendations prescribe treatments during broodless periods at temperatures between 35-61 degrees.

There are two methods used to vaporize (sublimate) OA, passive and active.  The passive method involves placing the prescribed amount of OA (1 gram/hive body) onto a mini battery powered heat plate that is inserted into the hive’s entrance.  After insertion the hive entrance is closed with foam or a piece of cloth and the electricity is applied. The crystals melt and sublime into smaller crystals that disperse within the hive covering the bees and hive interior.  All other entrances and openings such as cracks must be closed or taped shut so the fumes don’t escape and reduce treatment efficacy.  It takes approximately 3 minutes for the OA to sublimate and it is recommended that the hives remain closed off for 10-15 minutes after treatment.  There are several passive Varroa vaporizers on the market.  Examples include the: Varrox-vaporizer from Switzerland, Heilyser Technology vaporizer from Canada, Varroa cleaner from Serbia and Kiwi Vaporizer from New Zealand.  There are other home-made vaporizer designs marketed.

The other method of OA vaporization is the active method in which the OA crystals are heated within a container until sublimation occurs outside the hive.  After sublimation, vapor is blown into the hive entrance.  These gizmos typically require a heat gun, source of electricity and air compressor for some of the designs.   Lega bee supply from Italy markets one of the designs.  For some entertainment, do a google search on commercially available and homemade OA vaporizing contraptions.  Some of the designs featured on YouTube do not appear to be safe or effective!

As is the case with the OA trickle application, the efficacy of OA vaporization may be reduced when applied in cold temperatures when bees are in tight cluster since the crystals do not penetrate into the clustered bees.  Likewise, high humidity during treatment may reduce treatment efficacy.  Active methods of vaporization are said to work better than passive vaporization when bees are in tight cluster.

It is imperative for beekeepers to read the Oxalic Acid Dihydrate label prior to use and follow the directions.  Although OA is considered an organic mite control, it has a “Danger-Poison” signal word on the label meaning it is highly toxic and corrosive.  Beekeepers need to adhere to the personal protection label requirements and the personal protection equipment (PPE) statements.  Do not apply OA to hives of bees with supers in place so honey is not contaminated with this toxic substance.

Late fall or early winter Varroa treatment with oxalic acid is a valuable component for honey bee pest management.  The use, efficacy and safety are well-documented in Europe and elsewhere when used properly in accordance with label instructions.  With time and experience, Maine beekeepers will find that OA treatment fits an important need as a Varroa “clean-up” that will ensure healthy hives in spring. Please read and follow the label.  Remember, “The label is the law”.


February 2016 ABC Meeting Announcement

Chris beekeeping pic


The next meeting of the Androscoggin Beekeepers Club (ABC) will be held Wednesday, February 10 at the vestry of the West Auburn Congregational Church, 811 West Auburn Road, Auburn, ME 04210.  Note that we will no longer be meeting at Edward Little High School in Auburn.  Club business will be conducted from 6:30 PM to 7:00 PM followed by the presentation “Spring Hive Management for Maine Beekeepers”.

Our February speaker will be Chris Rogers of Backwoods Bee Farm in Windham, Maine.  Chris is an Eastern Apicultural Society (EAS) certified master beekeeper who has spoken to the Androscoggin Beekeepers Club several times.  He is a fantastic speaker and teacher who has generously agreed to speak to the ABC again.  As the co-owner of Backwoods Bee Farm in Windham, Chris plays a valuable role as a source of both information and beekeeping equipment.  During his presentation “Spring Hive Management for Maine Beekeepers”, Chris will describe the necessary activities beekeepers in southern Maine must consider as we enter Spring.

Chris’ ABC sponsored presentation is open to the public.

January 2016 ABC Digest

mitesondrone_14-05-08_0053_cropYouth Scholarship Available for Attending 2016 EAS Meeting

We have been asked to forward the following information regarding and application for a youth scholarship to support cost associated with attending the 2016 EAS conference being held in Gallway, NJ.

The Mann Lake Scholarship was established to encourage a worthy young individual to pursue an interest in honey bees and beekeeping.  The Scholarship will provide financial assistance for the selected candidate to attend an annual EAS conference.  In addition to the waiver of registration fees by EAS for the short course and the main conference, the Scholarship will provide up to $1,000 to the successful candidate to offset other conference expenses.

This year the annual EAS conference is at Stockton University in Galloway, NJ, July 25 – 29.

You can access the application form for this scholarship from the following link:

Please contact Peggy McLaughlin ( with questions.

It’s Time to Sign Up for Your Beginning Beekeeping Class

If you or someone you know is interested in taking a beginning beekeeping class (aka  attending a “bee school”), now is the time to find one and to register.  Most beginning bee schools are taught in late winter to allow new beekeepers to prepare for the upcoming bee season.

Several bee schools are listed on the Maine State Beekeepers Association (MSBA) Web Site which you can access from the following link:

MSBA Bee School Listing

In addition to the many bee schools listed on the MSBA site, the Maine Organic Farmers and Gardeners Association (MOFGA) is also offering a short beginner’s course in Unity, Maine at their Common Ground Education Center. For information about fees and registration openings, please consult the MOFGA events page.

Some Winter Reading About Oxalic Acid Mite Treatment

At our January 2016 ABC meeting, we spoke briefly about the fact that the EPA recently registered oxalic acid for use as an anti-mite treatment in honey bee hives. You can read about that here:

EPA Registers New Miticide to Combat Varroa Mites in Bees

As you begin your research on OA as a miticide, you will probably have a lot of questions. One thing that you will see is that 100% OA is available as an inexpensive wood bleach and some beekeepers have been using this for years. It’s important to be aware that the OA you might purchase from a beekeeping supplier (like Brushy Mountain) will be SIGNIFICANTLY less concentrated. If you decide to go the OA route, be sure you know exactly how to proceed to keep yourself and your bees safe. For some great information about this, I’d recommend the article “OXALIC ACID: EFFECTIVE & EASY ON BEES, BUT . . .” by Jennifer Berry published March 2015 in Bee Culture Magazine.  You can access the article online from the Bee Culture website.

If you are interested in a longer (but still freely available) read, I’d recommend the following Doctoral dissertation:
An Investigation of Techniques for Using Oxalic Acid to Reduce Varroa Mite Populations in Honey Bee Colonies and Package Bees” by Nicholas Aliano in 2008.

Don’t let the fact that its a doctoral dissertation put you off. This thing is very readable and contains some real data. To dig into the part(s) that interest you the most, just scan the table of contents after downloading the pdf.

During our group discussion at the January ABC meeting, I mentioned that Randy Oliver (writer of the popular beekeeping web site “Scientific Beekeeping: Beekeeping Through the Eyes of a Biologist“) has posted at length about his use of oxalic acid in his hives.

Randy recently updated a Powerpoint presentation he created about the use of oxalic acid. You can access the file and read some interesting information regarding OA treatments from his ScientificBeekeeping website.

If you’ve never visited the Scientific Beekeeping site, I highly recommend it. Note that this is not an endorsement of everything on the site, but I will say that there is a lot of interesting information and discussion about honey bees on the site.