Welcome aboard Bert.
Got a couple hundred acres in Lavaca County, probably not too far from you and I know about Flat Sedge too. It can be controlled using Grazon P+D and I'm told 2,4-D works pretty good too, but I haven't tried the 2,4-D. Both products are controlled so if you want to spray it yourself you will need an applicators license. Flat Sedge will take a place over in a heart beat and cutting it ( if you can) doesn't even slow it down.
Are you around POC/Pt. Lavaca?