I have two large lilac bushes, probably 20+ years old. I have only lived in the house for 4 years. Last year I noticed some blackening on leaves and flowers, but then the trees seemed to recover, I thought perhaps it was only frost damage. This year I am certain it is bacterial blight. Both trees seem affected all over. While there are still some blooms and green leaves, I am not sure how I can prune affected branches away without simply cutting down both trees to the ground, which I am willing to do if it will save them. I truly don't want the lilacs to die. They are 10+ feet tall. Is there anything I can do to save them?