Ask Mr. Smarty Plants

To answer your question, I contacted Eric Beckers, Forester, with the Texas A&M Forest Service Project in Austin.  He, in turn, asked for input from Courtney Blevins with Cross Timbers Urban Forestry Council that includes your area of North Central Texas.  Here is what Eric (and Courtney corroborated) said about your trees' problems:

"Our main threats to red oaks in North Central Texas are oak wilt, drought related secondary insects (borers) and diseases (hypoxylon), and urbanization (bulldozer blight).  Bacterial leaf scorch can cause chlorosis and dieback and is usually accompanied by a large amount of marginal burn and defoliation.  But far too often the chlorotic oaks we witness are ones that should have stayed in Louisiana or Arkansas where they came from.  In other words, their genetics were just not right for our high pH soils and they develop nutrient deficiencies that usually cannot be corrected.  These off-colored oaks are often less then 10-20 years of age and usually exhibit twig dieback and are typically short lived.

The answer is to plant trees grown from seed sources collected in a similar habitat or ecoregion.  Not always an easy task, but the best nursuries will most often carry plants that will adapt to their market's environment.  We should plant native Texas red oaks and possibly western seed source Shumard oaks in Central Texas, not East Texas seed sources or hybridized (another issue) red oaks that do best in more acidic and moist soils found the other side of the Sabine River."

Here is the Texas Forest Service link to diseases and insect pests.

You can visit the Texas A&M Forest Service Urban Forestry page to find contact information for the office in your area.

You can find the names and contact information for Certified Arborists in your area on the Texas Chapter of International Society of Arboriculture page.