Fairy rings are often associated with excess thatch, so reduction of thatch is the most useful approach to control. Try spiking, light topdressing, wetting agents. Only ProStar has a label for fairy ring and results have been very mixed. It may be easier to mask the symptoms with iron and light fertilizer applications. Many times the superintendents notice the problem more than the golfers.
Fairy rings are of little concern in lawns.
This is not a true fungus, but shows up suddenly and sometimes in great abundance. Many people are familiar with the bright yellow slime molds on bark mulches that mature to a beige color and black powdery spores. On turf, they generally appear slimy black in small areas and mature to light gray and black powdery spores similar to cigarette ashes. A quick diagnostic test for a slime mold is that it will be found on grass blades as well as any clover or other weeds in the area. The good news is that slime molds are saprophytes and eat only dead organic matter.