Around here in NB a 'final' treatment in early winter when broodless is stressed, but I always wonder about the efficacy of treatment when they're clustered. I am sure the remaining mites are in the middle of that cluster.
Not really a problem if you use a bit of common sense ( not insult intended) a fair 40/50deg day is fine. Its already a loose cluster, and your blowing in 350 air (yes it cools quick) so loose clustered bees quickly expand and move the OA around the hive (yes I have checked) good penetration is not a problem.
Been doing it in late NOV in my area for about 10 years now?? Nice cool 45 degree fall days.
As for midsummer treatments, returning foragers are only blocked for a minute or two, so its not a big deal. I block them longer parging the truck next to the yards!
It always amazes me they cant figure out a way around the truck!
Charles
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