How recently did you notice the leaf feeding? My guess is that is a caterpillar...just because they are the most common problems. Some are late season pests and others are earlier in the year. If you cannot find any caterpillars, I would guess the feeding is done and they won't likely get worse. If so, no treatment necessary.
The first picture, the white things sure look like cottony maple scale. While these pests attack more than maple, I cannot find a reference that lists hickory or pecan as a host. Probably a different scale (Lecanium scale is common on hickory, but not puffy and white like that). Get a better pic of those if you could. If that is the only place you see those, prune it off and dispose.
How bad will the mess the tree and how do you get rid of it?With those pics, I agree with @farmer steve more likely Pecan spittlebug rather than a scale.
I had them on my pecan tree a few years ago. (yes in PA).After some research they don't seem to pose a problem even for the commercial growers.How bad will the mess the tree and how do you get rid of it?
Free pecan wood is even better gunny.wow pecaN WOOD would make very good firewood \
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