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Trickle, Spray  or Vapourise?

By Dr G. Liebig and Dr K. Hampel

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Oxalic Acid treatments require the use of protective equipment for the beekeeper

Oxalic acid has had an astonishing career as an anti-Varroa treatment. At the start of the 1980's scientific tests indicated that the substance had little effect when sprayed as an aqueous solution onto combs occupied by bees (Koeniger et.al. 1983). Around this time the substance was being used in just this way with success against the Varroa mite in a number of States of the Soviet Union bordering on Asia. German nationals travelling from Kazakhstan to Germany brought information regarding this method back with them. The method attracted the interest of beekeepers (and scientists) after the "Association for Natural Beekeeping Methods" at Fischermühle in Rosenfeld in Würtemberg successfully tested the method and reported it in the German language beekeeping press (Radetzki et al 1994). From that time onward oxalic acid became a favoured alternative to lactic acid, which was also applied to colonies as a spray treatment. Scientific comparisons demonstrated that oxalic acid was superior to lactic acid in its effectiveness and tolerance by the bees, naturally it was necessary to consider effective user protection in its application. The user must take care to protect against oxalic acid vapour being inhaled or coming into skin contact. Oxalic acid as a spray was the `long time` standard treatment method used by the Beekeeping Research Dept at Hohenheim against Varroa in brood free colonies in late autumn or early winter.

The labour intensiveness of the method, which requires the withdrawal and spraying of each comb with bees and the risks to the user are probably the main reasons that this method did not immediately find favour with many beekeepers, in whom the opinion was that the opening of the hives at low temperatures in conjunction with the spray treatment was detrimental to colonies.

A ´watershed´ for oxalic acid occurred in 1995 when information from Italy indicated that a good result could be obtained using oxalic acid as a ´trickle´ treatment, whereby the acid was trickled between the frames onto the clustering bees.

The trickle treatment was rapidly accepted into anti -Varroa beekeeping practice. The fact that the mites dropped quickly after application of the acid without any indication of bee mortality gave the treatment even greater credibility.

This led many beekeepers to the belief that that the trickled oxalic acid had no adverse effects on the bees. This was soon found not to be the case. Numbers of beekeepers believe in the maxim ´lots achieves lots´ and used the trickle treatment many times and killed their bees - because the 5 - 8% acid concentration used in the spray method was tolerated badly by the bees as a trickle treatment.

The trickle treated bees become quite acidified at the first application and die early without showing on the floor board. Repeated trickle applications result in the colony literally flying itself ´bald´.

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