Some good news. It looks like the plants will survive and carry on. From beneath the level of the first branches I cut and what I've trimmed subsequently, a lot of new growth has erupted from many nodes. Although most of it is still small, it appears all of it is normal and not deformed.
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Many more of my plants had lighter damage so the vapor traveled quite a ways. I did learn something interesting from the farmer. He told me an opened jug of 2,4-DB can be left on the upwind side of a cotton field and the vapor will kill plants all the way across the field. It's some nasty stuff for susceptible plants.