Manhattan, Kan. — As summer rains fall across Kansas, many people may see mushrooms pop up in their lawns a day or two afterwards.
Kansas State University horticulture expert Ward Uphams said that while most of these mushrooms are harmless or even beneficial, those that form an arc-like or circular pattern called fairy rings can harm lawns.
“The ring pattern is caused by the outward growth of fungal mycelium,” Upham said. “They form a dense, mat-like structure in the soil that decomposes organic matter.”
Upham said the decomposition stimulates the growth of dark green or brownish grass around the outer portion of the fairy ring. However, the thick mat formed by the fungus underneath the grass interferes negatively with water availability.
“The fungus may also release certain byproducts that are toxic to the turf,” Upham said. “This may lead to dieback of the turf close to the ring.”
Unfortunately, fairy rings are difficult to control. One method Upham suggests is digging to a depth of 6-8 inches and a 12 inch width on both sides of the ring, then refilling those holes with non-infested soil. “This is a great deal of work and should only be considered in extreme cases,” he said.
Upham does not recommend fertilizing the rest of the lawn to match the dark green color, or the use of commercial-grade fungicides. He said those tactics may cause other problems to home lawns.
“Spraying a fungicide to the mushroom itself does little good,” he said. “Remember, the mushroom is simply the fruiting structure of the organism. Most of the fungus is below ground and inaccessible to the chemical.”
More effective methods may be to simply pick or mow them as soon as they appear.
“Removing sources of organic debris from the soil can help, if possible,” Upham said. “Also, mushrooms tend to go away as the soil dries. Patience may be the best control.”
Upham and his colleagues in K-State’s Department of Horticulture and Natural Resources produce a weekly Horticulture Newsletter with tips for maintaining home landscapes. The newsletter is available to view online or can be delivered by email each week.