One of the last bee work to do is treating your colonies with Oxalic Acid. Even if you had low mite counts into October, in my opinion this last treatment of Oxalic Acid is critical for winter survival. Hopefully your bees are now becoming broodless as the hive shuts down brood rearing. Late feeding may keep brood in the colony for a while yet.
To get the best treatment, beekeepers need a broodless hive. With no brood in the hive, all of the mites in the hive are riding on the bees. A treatment of Oxalic Acid during this broodless time, yields the best results. When there is brood in the hive, most of the mites are in the capped brood cells and the Oxalic Acid treatment is less effective.
Oxalic Acid treatments happen in late October.
The treatment is applied when it is a temperature of 40 degrees at the time of application.
The temperatures can warm up later in the day, but at the time of treatment, we want the temperature to be 40 degrees.
The reason for this is, the bees are clustered to a tight ball of bees when it is 40 degrees. The bees can easily be treated with the main cluster easily accessible. If it is warmer then 40 degrees, the cluster loosens up and it is harder to get all the bees treated properly.
There are two methods of treating with Oxalic Acid, the dribble method and using a vaporizer.
Do not use a bug fogger. A varroa vaporizer has been engineered for the treatment with Oxalic acid, a bug fogger has not been designed for mite treatments. The bug fogger does not have a way to measure proper dosing. With a fogger you could be killing your bees with to much Oxalic acid or you could be killing your bees with an ineffective treatment. Both scenarios are, your killing your bees.
Here are two videos of treating with Oxalic acid. Double click on the videos for full screen.
Dribble method, you are squirting the Oxalic Acid directly on the bees.
Using a vaporizer