This year some of my trees, shrubs, and perennials grew out leaves that were normal and healthy looking then leaves that were curling up to varying degrees, then later in the season normal again. No insects have been seen. Here are some pictures on my lilac.
It looks like herbicide damage. Was a herbicide used to kill off the lawn around the tree? If so, I think some of it must have been oversprayed onto your Lilac.
Thanks for your help, I did some more research into herbicide damage and found that it was most likely the dicamba in the spectracide I was using to kill the grass near my trees. I guess the dicamba can remain in the soil even though the product is supposedly safe for soil. I'm so happy to have figured it out, thanks again.
That can also be caused by a strong fertilizer like Miracle Gro, especially if you use it through the hose.
