Q.Lilac Tree
We recently planted a Japanese White Flowering Lilac tree in our yard. It appeared healthy when we purchased it a week ago but now it appears to have some leaves curling and turning black along the edges. We can see any insects or pest on the leaves that may be causing this to happen. The tree is in the sun the majority of the day and gets some evening shade.we live in zone 3. What could this be? Thank you

Lilac bacterial blight is one possibility. Being newly transplanted, the shrub is under stress and more likely to suffer from disease. Immediately remove affected leaves and stems and do not compost them. Prune your shrub so that air flow is good; i.e. don't let all the suckers grow and leave the shrub crowded. This also helps prevent powdery mildew which is common on lilac. Here is a gallery of photos of different leaf diseases. Research lilac bacterial blight and compare to these photos. Your local extension service may have an online or in-person plant clinic. https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/management-of-leaf-spot-diseases/