Source: "How to Band Your Tree - Cankerworm Prevention", GreenerDurham, YouTube
Those little green canker worms/inchworms LOVE to eat willow oak leaves. Many of our older oaks are at or past their peak, so any additional stress is dangerous for them. That is why it is time to put out tree bands, those sticky bands that trap the females as they go up into the canopy to lay the eggs. (Even what looks like a crummy job, like I did last year, will still catch a lot of bugs.) City arborist Alex Johnson recommends putting up the bands up when 90% of the leaves have fallen or before the first hard frost, whichever comes first.
The traditional method is you band your trees with a paper or burlap strip, then coat it with Tanglefoot, a gooey substance that the bugs try to cross and get stuck in. You do it about 4-6 feet off the ground–low enough for you reach comfortably, but high enough so Junior and/or Fido cannot reach. Stone Brothers has the stuff including Tanglefoot, which was in short supply last year. If you have questions about technique you can watch a video at https://www.youtube.com/watch?v=q-2HE6Oqi70 or check out this fact sheet at http://durhamnc.gov/DocumentCenter/View/953