Winter Varroa Mite Control

By Jon Parker,
18 January 2014.

Winter Varroa Mite Control

Do We Or Don’t We ?

It is always a dilemma. Do we treat or don’t we?…… Some put boards in and count the drop of dead mites, others will treat regardless and others will not treat at all. The best and surest method is to put boards in and then treat the colonies that are badly infested. That is great but we run a commercial operation so how do we manage it?

A Large Colony Gets The Fumigation Treatment.

The Big Decision

We fumigate once in the Winter regardless of infestation. In fact we don’t even check. What we do not do though is worry about it much in the Summer. We do not over medicate and this gives the bees a chance to develop resistance or their own mite reduction strategies. This might sound odd to a hobby beekeeper but we simply cannot devote that amount of time to a problem which in many cases will do us a favour; by removing weak populations from our gene pool.

When Do We treat?

We pick a nice day between Christmas and mid January, when the temperature is close to or above 9 degrees celsius. This allows us to fumigate the bees around midday so that a warm afternoon follows. This will enable the bees to re-cluster in temperatures that will allow it; do not try this close to sunset or you might have a disaster on your hands.

Cruel To Be Kind

The Fumigation Method

We make sure we have a fully charged leisure battery available before we start any fumigating. A leisure battery is used because it is low maintenance and can survive extremes of temperature between charges. The burner is filled with one scoop of oxalic acid crystals (approx 1 g) per brood chamber or one short scoop for a 6 frame nucleus colony. The burner is inserted into the entrance and the battery is connected for 2.5 minutes on an egg timer and the entrance is sealed with foam rubber. You will see the fumes leak out from the joints in some cases but that is a good indicator that the burner is working. Once the timer goes off we disconnect the battery and start the timer for a further 2 minutes. That allows any remaining acid crystals to off gas. The Burner is removed and quenched in water and the hive sealed once more for a further 10 minutes. We move the burner to the next hive and repeat the process. By doing this we need 3 egg timers. One for a colony having the 10 minutes of trapped gas, one for the colony getting the burner and one more on the next hive to get the treatment. There will usually be 2 colonies on their 10 minute phase.


This method will burn open brood and that is why we choose the weeks in the year when that stage is at its least abundant. We will also treat a few days after we have collected the colony if it is a swarm; but then we put in a frame of open brood afterwards to stop the new colony absconding. We were certainly right to do this treatment this year because of the mild temperatures. The mite populations might get racing away and be too big to tackle effectively with other treatments in the Spring, if we see the evidence of Varroa. Treating in Spring would set the colonies back at just the time when they need to be booming. You will get some losses by fumigation but we take the view that we could lose colonies by not doing a treatment at all. We will only treat in the Summer if we see the results of varroa infestation manifest in the form of follow-on maladies such as paralysis virus etc. Do wear a bee suit and all of the correct safety clothing, rubber gloves, mask and goggles. Although oxalic acid is present in Rhubarb, you certainly don’t want it present in your eyes.

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