Monday, August 26, 2013

Oxalic acid drip - varroa mite

There seem to be as many different ways of combating Varroa as there are bee keepers.    I found this one mentioned on Denmark bee keeper societies website.    I like it because it doesn't destroy the brood because of the fact that you do the treatment in the winter time, when there is no brood.    Does anyone have any experience with using this?  Being that it is found in nature and in honey naturally it seams to be a little less drastic then some of the other methods i have read about.  

Oxalic acid drip is extremely efficient, inexpensive and easy to use in that brood free period.

Oxalic acid is an organic acid, which is commonly found in nature. For example.  the sour taste of rhubarb and sorrel derived from Oxalic acidOxalic acid is also naturally occurring in honey.

For combating varroa oxalic acid is used in a very weak solution (3.2%). This solution is only very slightly corrosive. However, one must be extremely careful in contact with the skin as oxalic acid can be absorbed through the skin. Oxalic acid can also be dangerous if  breathing or ingested. Therefore it is not advisable to administer an Oxalic acid drip with a spray bottle.

The drip method gives you control of the oxalic acid.  It is how ever also recommended you use acid-resistant rubber gloves when administered the solution.   When mixing, use gloves, goggles and respirator (dust mask).

An increase in Oxalic acid concentration can be seen in the food stores, but this falls back to normal levels within 8 weeks after treatment.  There are currently no identified increased residues in honey season after application of Oxalic acid the previous winter.

There are to date not identified resistance to oxalic acid.  Why Oxalic acid works is not fully known. However, the spread oxalic acid is by body to body contact of the bees in a winter cluster.

Oxalic acid drip does not work on sealed brood, so the treatment must be carried out during periods of as little brood as possible. That is in the "Brood free" period in November / December.  In other countries, there has been a tradition to treat much later. However, one should treat as early as possible so that the damage done by the mites present is minimized.  In the past the best results where found in colonies who had at least one flight day after treatment. However, there are no studies that suggest that this is necessary.

To Oxalic acid treatment purchased oxalic acid dehydrate, which is a white powder. Oxalic acid di-hydrate is normally sold as oxalic acid.
Oxalic acid Treatment recipe

  • 1 liter of water 
  • 1 kg sugar: 
  • 75 grams of oxalic acid dihydrate. 
This is enough for 55 colonies.  Be careful not to mix small quantities, for example. For just two colonies,  weighing on ordinary kitchen scales can give an incorrect mixture due Kitchen Scales agree inaccuracy.

Swiss studies have shown that  Oxalic acid treatment can be stored in a basement (under 15 degrees), for up to 6 months.  If the mixture is kept at a higher temperature, the solution will become toxic to bees. We therefore it is recommend using fresh mixes. One should keep the solution in a child-resistant container.

Oxalic acid treatment should be lukewarm. Use a 50 ml syringe. Add it slowly  3-3.5 ml per minute, on the bees between the frames. This gives approx. 35 ml per minute. bee colony. This is a very small quantity, so it may be a good idea to first practice with water. It is important not to drip ​​directly on the bees and not just on the top of the frames where the bees will leave it alone.

Danish and foreign studies have shown that treatment to a bee colony more than once per. Bi-generation, there may be damage to the bees and thus reduction in hive strength. It is therefore recommended to treat a hive only once per. season. However, it is OK to treat again as long as there are several months between treatments. We have beekeepers who treat both fall and spring with oxalic acid.

By common Scandinavian trials and experiments in international cooperation "European Group for Integrated Varroa Control," which DBF has participated, achieved efficiency of over 90% in several studies.

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