Lilac Tree Has Olive Green Growth On Bark

Question From: ILLINOIS
Q: My Lilac tree has an olive green material that covers a large part of the bark/ what is this and how should it be treated?

A: My guess is what your looking at are lichens. They are not harmful to the tree and are relatively common on mature slow growing trees and shrubs. Google "lichens on bark" to find out more about them. Best And Happy Yardening, Nancy