Winter varroa treatment with oxalic acid

This week sees the shortest day of the year, time for winter treatment with oxalic acid.  My varroa treatment strategy has evolved over the few years I have been keeping bees.  I found this summer that two hives with very low seven day varroa counts still had evidence of deformed wing virus or phoretic mites so I have rather less faith in counting.  My plan now is to use a thymol-based treatment in August and oxalic acid in December, regardless of the varroa counts.  In this I have been influenced mainly by David Evans (https://theapiarist.org) and Rusty Burlew (https://www.honeybeesuite.com).  It is worth reading David's two recents posts on the why and the how of winter varroa treatment.  The direct link to the later of the two articles seems to be playing up but you can get to his blog here.

At this time of year we expect the bees to have little or no brood, important because oxalic acid does not get to mites in sealed brood.  I treated my bees on a cold frosty day earlier in the week, chosen so all the bees would be at home and well clustered.  The whole process is over very quickly so with my own bees there was no chance to take photos.  On the same day I met Sue and Ian at the local association apiary to treat the hives there.

I wrote about the dosing two years ago but using the recommended dilution of Api-Bioxal it works out at 5ml per seam of bees.  The oxalic acid is trickled from a 5ml syringe or a trickle bottle.  Here Sue is removing the crown board,

then charging the 5ml chamber in the trickle bottle,

and dribbling the 5ml along the seam of bees.

We have found it helpful to use a finger to mark the next seam to be done, so we don't lose track while recharging the bottle and miss out a seam or treat one twice.

Sue also trickled any bees hiding on the underside of the crown board.  All that remained was to replace the crown board, heft the hive, and add some fondant if necessary.

David Evans also recommends doing daily varroa counts over the next few days to check on the efficacy of treatment but otherwise the bees can be left in peace until next spring.