After the cleansing flight it should be evaluated if the colony needs to be treated for Varroa. To find out if the colony needs to be treated, count the number of dead mites on the bottom board over 7 to 10 days. If you find more than an average of 1 mite per day you should treat the colony.
* Oxalic acid. Trickling of 4 ml per fully occupied beeway on adult bees. VIDEO NEEDED
* Formic acid treatment. Recommended every 3 years to also treat for tracheal mite. Please note that formic acid can kill brood or even adult bees at higher temperatures.
* Drone brood removal in late spring and the beginning of the summer season. (LINK, no text here) Nordic brown bees usually produce fewer drones compared to other bees and drone removal is usually not done in breeding colonies. Drone brood removal is effective in removing reproducing mites, which also helps controlling the number of mites later in the season.