Practical Guide: 1.3.3 Vaporisation/Sublimation of Oxalic Acid

Vaporisation/sublimation of oxalic acid is a winter treatment recommended in Switzerland against varroa, provided that colonies are broodless or contain only open brood. Vaporisation is carried out using a dedicated sublimator/vaporiser device; correct application is essential for both efficacy and safety. The following summary is based exclusively on the official Practical Guide 1.3.3 (V 2511) of the SSA / BGD.

Official Practical Guide (BGD / SSA) – Summary

Practical Guide: 1.3.3 Vaporisation/Sublimation of Oxalic Acid (V 2511)

• Protective measures: Oxalic acid is strongly irritating and harmful to health; protective goggles, acid-resistant gloves, long-sleeved clothing, and a suitable respiratory mask (e.g. FFP3) are mandatory. Vapours and dust must neither be inhaled nor come into contact with the skin; do not stand in the vapour during treatment. Colonies are treated via the entrance.
• Required material: Vaporiser/sublimator (no cold fogger), Varroxal (Andermatt BioVet AG) or API-Bioxal (API’GENEVE Sàrl), respiratory mask (FFP3), stopwatch (for devices without timer), bottom board insert, grid-protected varroa insert, material to seal the entrance, container with water for rapid washing in case of acid contact.
• Important points: Sublimation is intended exclusively as a winter treatment; carry out only in broodless colonies or colonies with exclusively open brood (treatment is not effective in sealed cells). Good bee tolerability, efficacy approx. 95 %. Outdoor temperature: at least approx. 2 °C to a maximum of approx. 10 °C. If more than 500 mites fall within 2 weeks after treatment, the treatment must be repeated.
• Procedure (recommended):
  1. Seal open mesh floors with the bottom insert.
  2. Insert the grid-protected varroa insert.
  3. Put on protective clothing and respiratory protection.
  4. Fill the device according to the package leaflet (Varroxal/API-Bioxal).
  5. Position the vaporiser/sublimator according to the instructions for use.
  6. Seal the entrance.
  7. Perform sublimation according to the instructions for use.
  8. Keep the entrance sealed for approximately 10 minutes after completion.

► PDF of the official practical guide (DE)

► Official overview of practical guides (bienen.ch)
Note: Section Operational concept and practical guides → 1.3.3 “Vaporisation/Sublimation of Oxalic Acid”.

Summary based on Practical Guide 1.3.3 (V 2511). Last review: 01/2026.

Learn more:

• Practical Guide: 1.3.1 Treatment by spraying
• Practical Guide: 1.3.2 Treatment by dribbling
• Practical Guide 1.1: Varroa Concept
• Practical Guide: Recommended bee medicinal products