Spare the Scary Webs
If you have noticed some scary looking webs all over your trees, don't worry, it's just a late summer meal for fall webworms and they don't harm your trees. Put down the spray… their webbing will actually protect them from it.
Webworms are the harmless caterpillar form of native moths and only eat leaves that are nearing the end of their life-cycle, not new growth or buds. Because they are native, webworms have over 50 natural predators and many parasites that keep their populations in check so that you don't have to.
If you really do not want them, the best approach to control webworms is the “10-year-old boy biological control” -- poke a stick into the webbing, and pull the web and inhabitants out and jump up and down on them. Or even better, you can poke a hole leave the exposed web to become food for birds and other beneficial insects.