Greetings Sherry,
We've received a fair amount of phone calls this summer and early fall regarding early leaf senescence in hardwoods and conifers. Most of this, I believe, is do to the general lack of adequate precipitation this summer.
All along the I-57 corridor south of Effingham, one can see the hickories just browned-up and went dormant from drought-related stress.
Of course the pine issue you bring up could be nematodes, it also could be the result of many other contributing factors (which you also addressed). My recommendation to commercial growers is always to get a professional on-site to conduct an evaluation of the affected trees. This may include a seasoned and learned certified arborist, urban forester, pathologist, or even an entomologist.