Winter treatment of varroa with Oxalic Acid

DEFRA – managing varroa The fundamental aim of Varroa control is to keep the mite population below the level where harm is likely, (known as the economic injury level), therefore maintaining healthy colonies of bees for the production of honey and other hive products, and for pollination. It is not necessary to kill every single mite for effective control and it is not usually desirable to attempt this. However, the more mites that are left behind, the quicker they will build up to harmful levels again.

Phoretic mites are more vulnerable to treatment. Mites under wax cappings are hard to kill.

Drone Brood Uncapping

Key Fact When a colony has brood, around 80% of the mites are in the brood cells and only 20% are on the bees.

Good scenario Bad scenario Mite NumbersMite numbers January February March April May June point of July colony August 640 Treatment 6400 collapse September 50 October 100 November 100 December 100 January 10 Treatment

Mite NumbersAmount ofPercentage of sealed brood (cells)pupae In the colony affected by varroa January10000 February March April May June July August

Key fact The honey in a collapsing colony will be robbed out by neighbouring colonies. They will take home the honey along with thousands of mites from the collapsing colony. A healthy colony with a low mite count can reach a critical level of mites in a few days.

To treat 4 colonies Mix 100ml of water with 100 g of sugar Accurately weigh 7.5g of Oxalic acid dihydrate powder Add to the solution and mix thoroughly This will produce 165 ml of solution which should be enough for at least 4 colonies 5ml of the solution is trickled over each seam of bees, ie a colony with 7 seams of bees will require 35ml of solution.