Answer: I can't really diagnose the problem without seeing it. It could be a fungus, or it could simply be doggy spots. Or, it might be something more serious such as Fairy Ring. Fairy ring fungus is common in lawns in your area. It actually a mushroom mycelia growing under the lawn that is causing the rings. You may eventually see mushrooms sprouting up around the ring usually in spring. The only sure way to control the mycelia as it spreads is to dig out the turf and soil around the ring line to 2' deep. This sounds drastic, but the mycelia can really spread. The other thought would be to stop watering the lawn, especially in spring, so not to encourage the fungus. Hope this information helps you determine just what the problem might be!
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