Looks like you have fall webworms - see this BYGL webpage for more info. The "digital management" control option mentioned near the end of the article is the method I use.

BTW they look possibly planted too deep and with not enough area free of weed & grass competition. I now allow for 5' diameter, minimum. https://www.johnson.k-state.edu/lawn-garden/agent-articles/trees-shrubs/how-to-mulch-trees.html "Research has proven that, over time, a mulch ring placed 3 to 6 feet around the tree can almost double the growth rate of the tree."

I THINK .... some of the common wasp sprays used to be labeled for such ... but if its not on the label... dont do it ...

im not sure the branch is dead ... i would wait to see until next spring ...

they leave the nest to forage during the day.. return at night ... if they arent there at night.. they might already be gone ..

just take a stick and break up the webbing.. see if its repaired ...

ken