I recently got a panic call to check out a tree problem regarding a Texas Red Oak and/or a Spanish Oak. The client was extremely concerned about possible oak wilt or something killing her tree. Some leaves were totally dark brown and other had brown areas on the leaves, ( see photos below ) but no indication of oak wilt symptoms. It was obvious another problem and I first suspected either drought or too much water. Our area has suffered an extended period of drought, going into a third year. According to the US Soil Moisture Map, our region is in an excessive drought condition.
It was a small back yard and the tree completely shaded the entire area. The St. Augustine grass was plush and very healthy in appearance. However, drought conditions were not the problem, the tree showed indications of stress or a possible disease problem. I was unable to identify exactly what was happening so my best option was to contact Dr. Dave Appel of Texas A & M for a proper diagnosis.
Here is his Evaluation
I have seen similar symptoms many, many times throughout the state on red oaks. They are invariably found on red oaks growing in over-watered lawns, usually surrounded by St. Augustine grass growing right up to the base of the tree. You probably noticed the distinct iron chlorosis symptoms on the foliage. Again, symptoms of iron chlorosis are consistently associated with the syndrome and usually precede the necrotic scorching prevalent on the lower branches. What may be happening is that the oversaturated soil leads to rootlet mortality on the feeder root system of the tree, which in turn leads to micronutrient deficiencies such as iron depletion in the tree. We have lost red oaks on campus with the same symptoms. It takes years for a tree to go out, and I have also seen the process stopped by changing drainage and avoiding the over-watering. This tree doesn't look to bad, and I would guess there is still plenty of time to reverse the decline in health.
If any of this seems to be consistent with your situation, then I would look seriously at the water relations on the site and the potential for iron chelate applications.
I do not suspect oak wilt, or bacterial leaf scorch, are even remote possibilities.
The Back Yard Conditions
As I mentioned above that the St. Augustine grass was plush and very healthy in appearance and the entire area was completely shaded. The soil was very moist, indicating a well watered lawn. The shade aspect of course reduced the evaporation levels to a minimum and also the client reaffirmed that the watering schedule was excessive under these conditions. A result of love your tree to death.
A Little More Information
Iron chlorosis is a common generic symptom of over-watering. Overly wet or dry soils predispose plants to iron chlorosis. Iron chlorosis is more prevalent following wet springs, and where gardeners over-water in the spring.
In western calcareous soils, iron chlorosis can generally be avoided by eliminating springtime over-watering!
It is common for gardeners to allow sprinkler control settings to remain unchanged from the high summer water needs to the lower water needs of spring and fall. In this situation, the yard receives around 40% more water than is needed in the spring and fall. Changing the controller to meet seasonal needs will conserve water and correct iron chlorosis in most situations.