These spots have appeared on my lawn for the past three summers. It starts to appear during early July and starts to go away in the fall. It covers about a 16ft wide area and has some scattered spots in other parts of the lawn. This is a northern lawn, located in Michigan. Its has a underground water system and is on a 4 step Lesco fertilizer program. The rest of the lawn looks great except for these areas. The spots kind of look like somebody threw a firecracker in the lawn. here are three pics.