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 spaces between the combs 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 spaces between the combs 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 reaches only the mites sitting freely on the bees. Unlike formic acid, it does not penetrate the cell cappings. Trickling may therefore only be carried out when the colony is truly broodless. The classic date is the residual 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 on mites outside the brood.
To carry it out, the oxalic acid solution is warmed in a water bath to about 30 to 35 degrees, the sugar is stirred in and the finished solution is applied lukewarm. Depending on colony strength, this is 30 milliliters for weak, 40 milliliters for medium and 50 milliliters for strong colonies, i.e. around 5 to 6 milliliters per occupied space between the combs. The outside temperature should be at least 3 degrees, values up to about 5 degrees are ideal, but at most about 10 degrees, so that the bees sit tightly in the winter cluster and do not fly up. If the colony sits across two boxes, the upper box is tilted and both chambers are treated.
The most common mistakes are serious: treating despite remaining brood, checking for broodlessness only by spot checks, 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 hydroxymethylfurfural, which is toxic to bees and larvae, forms. The mite drop after trickling continues for several weeks, so checking the success requires patience.
Preparations containing oxalic acid are authorized as veterinary medicinal products and have since been exempted from the pharmacy-only requirement. For the preparations under standard authorization, the withdrawal period stipulates that honey may only be harvested in the following spring, so the late autumn treatment should be completed by 31 December. Oxalic acid is hazardous to health and highly corrosive; acid-resistant gloves and safety goggles are mandatory, and pregnant women should have no contact with it.
Sources (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