Winter treatment of varroa with Oxalic Acid

DEFRA – managing varroa

The fundamental aim of Varroa control is to keepthe mite population below the level where harm islikely, (known as the economic injury level),therefore maintaining healthy colonies of bees forthe production of honey and other hive products,and for pollination. It is not necessary to kill everysingle mite for effective control and it is notusually desirable to attempt this. However, themore mites that are left behind, the quicker theywill 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 Numbers Mite numbers

January 10 100

February 10 100

March 20 200

April 40 400

May 80 800

June 160 1600 point of

July 320 3200 colony

August 640 Treatment 6400 collapse

September 50

October 100

November 100

December 100

January 10 Treatment    

  Mite Numbers Amount of Percentage of

    sealed brood (cells) pupae

    In the colony  affected by varroa

       

January 100 0 0

February 100 2000 5

March 200 6000 3

April 400 12000 3

May 800 20000 4

June 1600 20000 8

July 3200 15000 21

August 6400 8000 80

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 powderAdd to the solution and mix thoroughlyThis 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.