Oak wilt is a fungal disease that affects the water conducting system of red, white and live oak trees. This disease was discovered in 1961 in Dallas but wasn’t diagnosed definitively until the 80’s. It had the potential to be the most destructive disease in the US but has been most devastating in the state of Texas. We are just past the worst time to prune oak trees, February to June. Wounds can be an entry point for the sap eating beetle. You can paint the branches you prune with even an inexpensive latex spray paint. Oak roots can clone an overlay another root system so this disease can spread as far as 200 yards away. The veins of the leaf turn orange so this is you first indication that the sease is present and this disease spreads and kills the tree quickly so preventing it from spreading to other oaks is most important. Removing and burning the tree is best as heat kills the fungus. Texasoakwilt.org is a good website to learn more.
Texas A & M AgriLIfe has a handbook that lists all the diseases including many funguses of different species of trees in Texas. Your local agriculture extension office is a good source to help you diagnose the problem. You can send them a picture or take in a sample.