I was considering doing an oxalyic trickle, just to help out. I removed one bottom screen, and found a few mites, so I thought about it, but wasn't so sure about the damage of lifting lid and exposing them to cold, disrupting the cluster. I would rather not have to treat with anything closer to spring to avoid hurting brood or queens. Our temps here are -1 and hovering around there most week.
Temperature today, 6:00 P.M. -- Abbotsford weather station -- +6 celsius.
Steve, in our fall management course at the Honeybee Centre, John told us that we should do our oxalic trickle ON DECEMBER 1. If many of the beekeepers in our area did this treatment AT THE SAME TIME OR CLOSE then the varroa problem would be minimized in our locality. But it is unlikely that this was followed through with everyone, of course. But that is life.
Oxalic acid is trickled when there is no brood or minimal brood present. It will kill brood. that is why it is done when it is COLD outside.
Finsky has advised to let the bees be in peace during the winter cluster time. I believe that he is right. If you saw mites when you removed the bottom screen, then you probably will definitely be needing to treat. I would think that there are quite a few. But please, do not think that my word is gospel, that is only an impression I get with this dreadful bloodsucker.
If you feel that you want to treat now, I would put the question out there on the forum whether to drizzle over the cluster. The small amount that is drizzled is too small to chill the bees. You only have the inner cover off for less than a minute to drizzle, so I don't think that the bees would be overly chilled.
I would think though, that maybe you could wait for a little longer. As far as I understand the varroa requires brood to live inside the cell to feed. So, the problem I see is that when the brood begins to be laid by the queen (and I think that can be happening pretty soon around here Steve), then these varroa will enter the cell and then the new babies will be born deformed and useless because of the destruction the mite does to the brood in their cell.
I don't know. Why don't you ask Ron, or call John at the Honeybee Centre to see if you should trickle NOW before brood rearing begins. We must ask questions to understand and take care of our bees properly.
Notice our weather today is +6 celsuis? We are not in that cold stuff that we were in even yesterday.
Hope that your question will be answered and I may have offered some insight. Great day. Cindi