I'm in Kansas City Missouri. This is year old sod that seemed to get through last summer just fine. Last two weeks have been mid 90's and I get this. I had one patch that was irregular shaped and local grass place said it was a fungus. Used their fungus stuff and it quit spreading. I have been watering the 2 zones that encompass the backyard every night for weeks thinking it was a water issue. It's been suggested to water in the morning for a little longer so I've switched the programming to accomplish that. Still has this look to it. Some of the dead spots have not a lot of soil depth. All the rest has at least 4". Took these pics to same grass place and they were stumped. Still not sure what would cause the straight lines. Thanks in advance.