I've had problem with my Star Magnolias.. basically, clumps have appeared on the branches..when you scrape them, a gray powdery substance pops comes out. For whatever reason, bees are swarming all over my trees..I sprayed two of the trees and now appears that I may have killed them. The 3rd tree is completely infested with bees but I've yet to spray for fear of killing it. Does anyone have idea what I might have? How to rid the bees? These trees are 10 years old and have been great until now.