Evidence of the Maple Petiole Borer has generated several requests from people in Manlius and Cazenovia to have their Maples inspected. I have also observed it at Colgate University in Hamilton on several small- to medium-size Sugar Maples. This is typical for our area from late May through early June, and seems to occur randomly from year to year, appearing on some trees and not others. Seeing green leaves suddenly fall off their tree can cause homeowners great alarm and a little bit of a nuisance with leaves on the lawn. Fortunately, it’s not a serious threat to tree health and usually will last for about one week. I found the University of Minnesota Extension Service technical brief on this pest to be well written and helpful for more understanding of this occurrence.