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.
LS