White Spider web on Tree
The webbing you see is caused by the Fall Webworm. This insect has two generations per year, one in spring and a larger one in fall. The damage inflicted by the caterpillars is minimal although the infested tree looks unattractive for a period of time. If you can reach the webbing, simply disrupt it with a stick and expose the caterpillars to birds. It is not practical to spray these insects unless they attack a small tree that has not become established.