I don't know but I have had the same problem here with evergreens for years not. Lower branches start to die and each year a few more progress up the tree until the whole thing is dead. I've tried cutting the dead ones off but it made no difference as the slow death of the tree continued. On the positive side I see a tremendous amount of little volunteer evergreens coming up. I've transplanted a few of them and they seem to do well. So far anyway.