Do you do any more than once a month? I did PS treatments this August and Sept. and I did them three days running, not sure why but I think it was because of a discussion on Randy Oliver's site. It would be nice if once a month kept the mites at a manageable level, the third day the bees are a little grumpy.I've used powdered sugar on each comb of bees each month in all my hives since 2013 and have not noticed any brood kill. You are sugaring the live bees, not the comb or open brood so if applied wrong, you certainly could gum up the works. I use a one hand Oxo sifter. I pull each bar (I'm 90% topbar hives) and upend it and park one corner of the bar on the top of the hive and tip it slightly. Dust that side, tip it back the other way and dust the other side and replace it. (I do make a point to look for the queen so I can be extra careful that she doesn't accidentally get dusted off the comb and onto the ground.)
Once a month, every month I can work the bees, which is 10 months out of the year, is enough to keep the mites in check for me. If I do notice deformed wing on workers or even spot mites, I might do it weekly for 4 weeks to get things under control in that particular hive, but I've only had to do that twice since I started keeping bees in 2013.Do you do any more than once a month?