One of our hives, formerly the strongest of three, has been weakened substantially by varroa mites. We've been treating with FGMO and see signs of recovery, but we're still not convinced they'll make it through the winter.
At it's worst, they seemed to stay to one side of the hive. The left half of the hive (a D.E.) looked like a ghost town.
We're wondering if they might winter better in a nuc.
Weather-wize, we live in Northern California near the Klamath River, close to the Oregon border.
Any advice would be appreciated.
Since you can't actually BUY a DE Nuc you'll have to make one if that's what you decide to do. Are you saying they are in a cluster in only one box on one side? I'm not sure how many bees you actually have, but bees basically want to winter in a ball and one box might do as well as two if there are not many bees. If this was a strong hive it's hard to imagine it's so weak you'd put them on only five frames or so for the winter. If you have acutal empty space (no honey or drawn combe etc.) then I would limit the hive some. They can't eat empty comb and they don't need the stress of keeping it warm.
There are several ways to limit the size. One is to buy a DE hive and cut it down to make two 5 frame boxes A normal DE is 11 frames and you have to come out exact or the bees will get back into the space around the ends of the bars, so if you want to make it into two you'll only get 5 frames. To do this you'll have to make two ends and cut the sides down.
Another is just put them in one box. Another is put something (foam insulation board would work) against one side to take up room. 1 1/2" foam would be almost just right for one frame in the hive.
Personally I think I would build a double screen board (see plans on this web site) in DE dimensions and put them on top of a stronger hive. Since it's a DE you'll have to build it because the only ones you can buy are Lanstroth dimensions.
It's hard to say how much room and stores they need for the winter, but I figure about twice the size of the space the cluster takes up filled with honey should probably get them through the winter.