Curling leaves on lilac
What is causing the leaves of my lilac to curl?
El Paso County Colorado trees and shrubs
Your same question was asked last year. I am providing a link to information about a possible cause - http://extension.usu.edu/files/publications/factsheet/eriophyid-mites2010.pdf. There is a microscope at the El Paso County Extension Office. You may wish to verify the mites are the cause by visiting the office along with a sample of curled leaves. The office website is http://elpasoco.colostate.edu/hort/hort.shtml.
Thank you for your question.