Trees, Shrubs and Conifers: 15 yr old white lilac sickly, 1 by anastatia

anastatia wrote:
This is a photo of a branch of the sick lilac bush. There are no tiny holes @ the base of the trunk(s) suggesting borers. I took a sample to local garden store and the 1st guess was stress due to hot weather. Only 2-3 of the 9 trunks/off shoots of this shrub are sick. So then he guessed a root disease. I treated it w/ Bayer product for disease. I noticed this AM another lilac on the other side of the yard is showing same thing. 1/3 of the bush trunks are sick.