It could be that you have dogs that like to pee in roughly the same spot every day. If that is the case you can treat the area to applying table sugar to the area at a rate of 15 pounds per 1,000 square feet.

Or, the spots are where water accumulates after irrigation/rain. If that is the case, then you have a fungal disease that will not clear up until next April.

When were the last two times you fertilized and what did you use?

What is your watering schedule (frequency and for how long)?

Check for army worms.