The first 20 feet on one end of a 50 yard row of mature lilacs bushes started to brown up in June, with leaves dying. Please see pictures. We planted these lilacs 25 years ago and have never seen them brown up and die in the mid summer like this. Lack of moisture isn't the issue. We also planted a new lilac bush among the dead growth, hoping it would fill in a gap we had. That wasn't a good idea obviously, because it too is showing brown, dead leaves. Looking at the pictures, can you diagnose this, or do we need an arborist to visit and confirm the disease? Thanks!