Ask Mr. Smarty Plants

We are assuming you were referring to an earlier question from Gregg Co. Texas, with the same problem. Aside from the fact that this has been a very hard year, even in East Texas, for heat and drought, there are several other things that can cause yellowing. If you just recently planted the oak, it could be suffering from transplant shock, especially if it was planted in the heat, rather than in mid-winter, when the tree would be semi-dormant. Yellowish leaves could indicate chlorosis, or lack of iron being taken up by the tree from the soil. This is often caused  by poor drainage and/or dense clay soil, which causes water to stand on the roots. Again, this could  be a problem caused by planting, perhaps without any organic material added to hole, or damage to the tiny rootlets that take up water and trace elements, including iron, from the soil. From a distance, we have no way of diagnosing your tree's problems, nor of recommending a solution. You say you know you don't have oak wilt, but we hope you did look at the link to identify it in that previous answer.

Your best bet for finding out what is wrong with your oak and how to treat is to contact the Navarro County AgriLife Extension Service agent, the Texas Forest Service or consult a professional arborist.