With all due respect. You asked what was killing your turf and unfortunately its you. The type of irrigation practices you described leads me to believe you set the stage for this poor performance. You probably had the classic rain help making it look as though you were doing a good job but when the real dry weather settled in...the errors of your ways were exposed.
Someone needs a good lesson in herbicide applications also.
Before you take in more responses. Make sure you get the better pictures for responders. Pulling up a couple of runners trying not to damage the roots. Lay them on the blacktop to ensure visibility so all can see the nematode activity before they give any product suggestions. I can not suggest any products at this time or tell you if these areas will survive. They can but unless you get proper cultural practices implemented most products will give false hope.
Start with correcting your irrigation management as well as keep that blade sharp and HIGH.
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