Good Morning Diane, 

Thank you for contacting the U of M Extension Service. 

Please click on the following link from the U of M Extension Yard and Garden website: https://extension.umn.edu/news/understanding-fairy-rings-your-lawn

This information states: 

What should you do with fairy rings in your lawn? The good news is that fairy rings do not kill lawns and are mainly cosmetic. They often disappear naturally. Waiting is usually the simplest management option.

Good Luck!

Diane, 

I would suggest you go to the spots, inspect the turf, see what is different with the spots as opposed to the lawn you are happy with.  Is the soil beneath the sod different?  Are these spots that appeared from taking down trees or something in the past?  What happens when you apply fertilizer? Do the spots disappear or change? If the spot has been there for 10 years, what have you done in the past? 

Here is a link to the annual lawn care calendar from the U of M Extension Yard and Garden website: https://extension.umn.edu/planting-and-growing-guides/lawn-care-calendar

Here is another link to consider planting something besides turf grass: https://extension.umn.edu/yard-and-garden-news/extension-research-help-you-help-pollinators

Good Luck!