For issues with South Texas Lawns I always recommend submitting a sample to the Texas Plant Disease Diagnostic Lab (https://plantclinic.tamu.edu/).  Analysis often reveals multiple issues, including lesser known fungal pathogens and pests. A proper diagnosis is very important to treat it effectively.

Submit sample Texas Plant Disease Diagnostic Lab

• Plant Disease Diagnosis Form

Common Lawn Issue Publications

• How to Diagnose and Manage Large Patch Disease
• Take All Root Rot
• Warm Season Turfgrass – Urban Landscapes
• White Grubs in Texas Turfgrass

More Helpful Links and Publications

• Aggie Turf Publications
• The Weed, Insect, and Disease Control in Turfgrass guide
• Turf Grass Cultivation