The yellow patches can be caused by a number of different things including summer patch type diseases like yellow patch and summer patch, or damage from a chemical applied to those areas, or from a disease called take-all patch. I suggest you contact your Harris County Extension Office and see about brining in a photo and a sample from the yard showing the sick turf. They can then recommend an appropriate remedy:
The following is their contact information:
3033 Bear Creek Drive, Houston, TX
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