Q.What Has Happened To My Lilac
I have several large lilacs ,but the purple ones this year have hardly any leaf on them but some flowers , one white one next to them has one branch starting to look sick , they all usually flower lovey
Certified GKH Gardening Expert
It could be disease like bacterial stem blight or pests like the oystershell scale or borers, all of which can cause defoliation. Read the articles below and they should help you pinpoint the cause.
It also looks like your trees need a pruning. An annual pruning can help keep your lilacs healthy.