The confectionary sugar should be applied/sprinkled on all the frames with all the bees on the comb, one by one, both sides and is quite a chore. Two hands are not really enough to do this gracefully. Better to be two people, one pulling and holding the frame and the other sprinkling the sugar. The sugar does not sprinkle readily and I used a strainer with a fairly fine mesh, shaking it constantly. A flour sifter would be better IMO. Best to try different methods prior to starting to see how - to - do best.
The idea is to coat the bees with the sugar and let them groom each other thereby dislodging the mites, making them drop through the screen bottom boards? The bees will eat the sugar and it is a feast for them, or, so I observed when I did this and I really did not see any mites suddenly drop onto the slide out boards placed under the screen bottoms in my hives.
I also did the liquid sucrocide treatment. That treatment requires a sprayer and the idea is once again to coat, lightly, all the bees, comb, brood, pollen, honey, frames with the liquid. This work is best done with four hands also. However warm weather is required. There is some info posted on the forums, this one, and others, about sucrocide treatments. The sucrocide is a Biochemical Miticide and is suppose to be safe as opposed to synthetic chemicals? Furtermore, spraying is easier than sprinkling dry sugar. DO NOT GET CARRIED AWAY WITH THE SPRAY!!!
There again I cannot say how effective this sucrocide treament was. I didn't notice an increase mite drop either.
In any event warm weather is required, for both treatments, because doing a two deep box setup, going through all the frames requires some time and you will not want to overly expose your hives to the elements if there is brood in them. DO NOT CHILL THE BEES PLEASE!!!
Personally, I am chemical free, so far, but I don't have much experience to go on so time will tell.
You should remove all non wanted comb from your boxes, frames, wherever, periodically to stay ahead of the bees who pretty much like to do things their way, sometimes. Keeping the brood box frames, 10 of them, close and tight against each other helps in burr comb prevention I have found.
Hope this helps. Jack