We had 3 healthy burning bushes planted 5 years ago. For the first 3 years, all was fine. Then last year one of them spouted few leaves in the spring. This year, the other two have done the same. I prune them significantly each fall. Also this year, I noticed a black sooty substance all over below one that had not spouted many leaves. Any suggestion? I have sheered off all branches with no new leaves.
