Q.Lilac bushes have brown and black spots on their leaves and are dropping leaves and thinning out. The dropped leaves are black
These bushes are over 40 years old. We never had to water these before but now with the current high temperatures in Virginia, we have begun to water the bushes. The ground is a dark brown when wet and a light brown when dry. The ground is a dark brown. But we have started to water them anyway.
Certified GKH Gardening Expert
They probably are getting too much moisture and humidity. Pick up the dropped leaves and destroy. Also, let the soil dry out some between waterings.
Your leaves look they could use some fertilization. And your trees could stand some rejuvenation pruning in early spring.