Varroa: The safe strategy
The varroa mite is the biggest threat to honey bees in Denmark. Without treatment, the number of mites roughly doubles every month.
Four seasons
- Spring (April to June): Remove drone brood with a drone frame every 3 weeks.
- Week 25: Count the natural mite drop for about a week. Under 1 mite per day is fine. Over 8 mites per day: treat immediately.
- Summer (early August, after the last harvest): Treat with e.g. formic acid, thymol or oxalic acid strips. Count the mites during the treatment.
- Winter (December): Oxalic acid trickling when the colony is broodless. Under 200 mites in the drop is low.
If more than 1,000 mites dropped during the summer treatment, give an extra treatment at the end of September or in October.
How to count
Put a varroa tray under the hive, ideally with a thin smear of cooking oil so the mites stay put. Count after 3 to 7 days and divide by the number of days. Record the count in the app and it will work it out for you.
Did the treatment work?
Count before the treatment and again three weeks after it ends. The drop in mites per day is the treatment's effect: over 90% is good, 70 to 90% is moderate, and under 70% means you should count again and give an extra treatment, preferably with a different product. Once both counts are recorded in the app, the effect is calculated and shown on the treatment in the hive's history.
Rotation
Synthetic products (tau-fluvalinate in Apistan, flumethrin in Bayvarol, amitraz in Apivar) must not be used year after year, or the mites develop resistance and the treatment stops working. Change the active substance from year to year, or switch to organic acids and thymol, which mites do not become resistant to. The app warns on the hive if the same synthetic product has been used two years in a row.