A lilac bush was destined for removal and I separated as many cohesive root and shoot bunches as I could. I planted some immediately and potted others, almost all of which are doing well. I notice one in particular has a white powdery substance on the surface of most of its leafs, which appears to have spread over the course of a few days but then more or less stopped changing its extent. Wiping it off with my fingers, it comes off pretty easily. I separated it from the other trees and took some photos:
In the last image to the left of my thumb you can see some of the powder I rubbed off with my thumb. It didn't have a noticeable smell.
Any idea what the substance is and how I should respond to it for the plant's health?