From the Facebook of:
Wisconsin Horticulture – Extension

Have you noticed your lilac bush looking pretty ragged lately? It may be Septoria leafspot disease, which is common throughout Wisconsin at this point in the growing season.

If you see irregular brown spots on your lilac leaves, or notice leaves have turned entirely brown and dropped off the plant, your plant may be infected. But is this disease a death sentence? Not exactly. Read our latest article about managing Septoria leafspot on lilacs https://go.wisc.edu/ge0422