Sometimes unexpected problems literally pop up in the turf. In this case, the ornamental grasses, planted as shrubs, have migrated and adapted to the turfgrass. This creates unsightly patches of grass which essentially ruins the turf. There are some selective herbicides that may or may not work or mechanical removal may be necessary. Only certain grasses do this, so do your research before planting a variety. You can also try mowing turf short in these areas as it may not tolerate a close regular mowing practice. You never know what problems mother nature is going to create, but if your persistent you can usually find a remedy.