Oxalic Acid Trickle Method
Behandlungsmittel
In the trickle method, an oxalic acid solution, to which sugar is added immediately before application, is applied evenly to the bees in the occupied comb spaces using a syringe or dosing bottle.
In the trickle method, an oxalic acid solution, to which sugar is added immediately before application, is applied evenly to the bees in the occupied comb spaces using a syringe or dosing bottle. The added sugar increases the viscosity, so the solution adheres better to the bees, and the mites are exposed to the acid for longer. This is the main reason for the good efficacy of this method.
Oxalic acid is a contact acaricide and only reaches mites that sit freely on the bees. Unlike formic acid, it does not penetrate through the cell cappings. It may therefore only be trickled when the colony is genuinely broodless. The classic timing is the final mite treatment in late autumn or winter, in practice about three weeks after the first frost period, usually between mid-November and the end of December. Efficacy rates of over 90 percent are achieved against mites outside the brood.
For application, the oxalic acid solution is warmed to about 30 to 35 °C in a water bath, the sugar is stirred in, and the finished solution is applied lukewarm. Depending on colony strength, this amounts to 30 milliliters for weak, 40 milliliters for medium, and 50 milliliters for strong colonies, i.e. about 5 to 6 milliliters per occupied comb space. The outdoor temperature should be at least 3 °C, ideally below 5 °C and no more than about 10 °C, so that the bees sit tightly in the winter cluster and do not fly off. If the colony occupies two boxes, it is tilted and both compartments are treated.
The most common mistakes are serious: treating despite residual brood, only spot-checking for broodlessness, overdosing, and above all repeating the treatment. Multiple applications or higher concentrations lead to markedly poorer overwintering and can cost colonies. Combs and frames should also not be wetted unnecessarily. The prepared sugar-containing solution is intended for immediate use only, because over time it forms hydroxymethylfurfural, which is toxic to bees and larvae. Mite drop after trickling continues for several weeks, so assessing success requires patience.
Oxalic-acid-based products are approved as veterinary medicinal products and are now exempt from the pharmacy-only requirement. For products under standard authorization, the withdrawal period states that honey may only be harvested the following spring, so the late-autumn treatment should be completed by December 31. Oxalic acid is hazardous to health and strongly caustic; acid-resistant gloves and safety goggles are mandatory, and pregnant women should have no contact with it.
Quellen (4)
- BfArM: Wortlaut der Standardzulassungen für Bienentherapeutika (Monographie Oxalsäuredihydrat-Lösung 3,5 % ad us. vet.)
- LWG Veitshöchheim, Institut für Bienenkunde und Imkerei: Träufelbehandlung mit Oxalsäure
- LLH Bieneninstitut Kirchhain: Infoblatt Varroazide
- Varroose-Bekämpfungskonzept Baden-Württemberg, Landesanstalt für Bienenkunde Hohenheim, Stand 11/2024