Sounds like mealy bug scale to me. Cutting the plant back was a good idea. Just don't compost the clippings and now clean up around the base of the plant. In the spring, clean up around the soil again adding a fresh mulch to seal in any tiny eggs that may have fallen to the ground. I think you'll be fine next year - insects arrive in waves and stressed plants - from dry soil or poor fertility are more likely to become infested. Keep growing, Marianne Binetti P.S. I got to visit Russia this summer - watch for my photos to be posted on this site soon. I kept looking for Russian Sage.