Here are a couple of great pictures from Nicholas May of True Green lawn care in Des Moines. These pictures were taken south of Des Moines this week. The disease is summer patch, caused by (Magnaporthe poae).
For more information on this disease, search "summer patch" in older editions of this blog.
Summer patch requires systemic fungicides applied before symptoms develop. If you have a condition like this that has already developed, you will need to core aerify in late summer and let it recover. Watering the area next year will help and systemic fungicides applied before symptoms develop next May will help. There is no reason to treat it with fungicides at this time.