I live in NW Florida, 1 mile from the beach. We've had a medium sized oak in our yard for 7+ years now and within a week/two weeks, it suddely turned brown and died. We cut it down and there was no fungus, no bugs, no visable signs of what happened. About 15 ft away from it we have two small scrub oaks that are dying too? We have not disturbed any of their root system, no pesticides, etc.