Rust on lilac
It looks like the lilac leaves have had a spider mite outbreak. If possible bring a leaf or two from each plant to our Master Gardener plant clinic to view with our microscope for evaluation. We want to verify the issue before having you spray anything. If it is a spider mite issue we can advise you how to control them. Usually a good soaking spray of neem oil, Safers soap, or horticultural oil will control them. Once the leaves fall off in late fall, rake them up and dispose of them to minimize the egg carryover to next season. Spider mites on plants can mean the plant was under some stress.