I am concerned about the post oak trees around me that are turning brown and dropping their leaves. This is happening in Oklahoma and Arkansas. I have contacted a local extension agent and the forestry service but they tell me it is just the oaks way of protecting themselves during a hot summer. I believe there is much more to this because there are patches of these together that are not in a rocky, dry area; there are also swaths across hillsides and streaks that run in a path. Could this be oak wilt?

Could be I suppose.

Your best defense is a strong organic program which encourages fungal growth in the soil (no fungicides or sulfurs). Spray the trunk, branches, and foliage with milk, molasses, and soap periodically to keep the beneficial microbes outside the trees healthy.