Oxalic Acid
Lexikon
Oxalic acid is an approved active substance against the varroa mite and the usual active substance for the winter treatment, the so-called residual mite removal.
Oxalic acid is an approved active substance against the varroa mite and the usual active substance for the winter treatment, the so-called residual mite removal. Unlike formic acid, oxalic acid does not penetrate capped brood. It only reaches the mites sitting on the bees. From this follows the single most important rule: oxalic acid may only be applied to a broodless colony. In a colony with brood, most of the mites remain protected under the cell cappings, and the treatment largely fizzles out.
There are three ways to apply it: trickling into the occupied comb spaces between the frames, spraying onto the bees, and vaporizing, also called sublimation. The widespread claim that vaporizing is banned in Germany is outdated. Since September 2023, an oxalic acid preparation has for the first time been approved as a veterinary medicinal product in Germany that may explicitly also be used for vaporizing, though only in a broodless colony and only with the equipment named in the approval. The Federal Office of Consumer Protection and Food Safety (Germany) points out that effectiveness depends strongly on the technique of the vaporizer, because oxalic acid decomposes instead of subliming if the temperature is too high.
Vaporizing produces fumes that are dangerous to humans. The approval documentation therefore requires long-sleeved clothing, acid-resistant gloves, safety goggles and a respirator mask, as well as attention to wind direction. Anyone who mixes their own solutions or uses equipment that is not part of the approval is acting outside the approved framework.
A winter treatment is not a mandatory program but a decision based on infestation level. As a guideline, the institutes cite a natural mite drop in late autumn of about half to one mite per day, above which residual mite removal is advisable. Unnecessary or repeated applications at this late point in the season harm the bees more than they help. A withdrawal period also applies: after a winter treatment, honey may only be harvested during the following year's nectar flow. Every application of a veterinary medicinal product must be documented.
Quellen (4)
- LAVES Niedersachsen: Was man über Varroxal 0,71 g/g Bienenstock-Pulver wissen sollte
- BVL: Hinweise zur Anwendung des Tierarzneimittels Varroxal
- LAVES Institut für Bienenkunde Celle: Leitfaden zur Varroa-Bekämpfung (PDF)
- Arbeitsgemeinschaft der Institute für Bienenforschung: Varroa unter Kontrolle (Broschüre, PDF)