Lilac receiving too much water?
Is it possible this lilac received too much water and now has some kind of fungus? Other lilacs in the garden which were planted around the same time appear to be fine, this one is on the border with a neighbor who frequently has a sprinkler going to water the lawn. Thanks for your help
We have received a lot of questions this season regarding lilacs and leaf browning and drop. The symptoms you are observing on the leaves are quite common on lilacs at this time of year. Lilacs are susceptible to bacterial and fungal diseases in wet spring weather. It is recommended you manage through cultural practices such as pruning to promote better air circulation and minimize leaf wetness. At the end of the growing season, clean up and discard in the trash (not compost) the affected plant material. https://extension.umd.edu/hgic/topics/bacterial-blights-lilac
Lilacs are also susceptible to borer damage which can cause dead and dying canes. You can look for holes in the bark. All you can do is prune back to healthy tissue. https://extension.umd.edu/hgic/topics/borers-shrubs
Lilacs also require pruning for best growth. They can get leggy and unattractive. You can and should prune old wood from lilacs on a regular basis to stimulate healthy new growth and flowering. The rule of thumb is to cut back no more than 1/3 of the plant at any one time, removing the oldest wood first. Wood that is too old ceases to flower well. The younger shoots that regrow will flower better (once mature enough) and are not as attractive to pests such as lilac borer.
Below are links to a video demonstrating the procedure and a description of how to prune:
Once the lilacs have reached a more youthful, vigorous state, such drastic pruning will not be regularly needed except to periodically remove aging stems here and there. Maintaining full sun exposure (6+ hours a day in summer) also will help your lilac flower to its fullest potential. If you are able to prune any nearby plants that might be shading the lilac too much, that can also help to improve the conditions for your plant. Make sure mulch is no thicker than several inches and keep away from the base of the stems.