Fairy Ring disease is found throughout Canada. The name, however, has a far older English origin, and refers to the superstition that small mythological creatures used to dance in small rings on grass leading to compacted circular bare zones and the mysterious production of mushrooms virtually overnight. We now know that there are several types of fairy rings (dead rings, stimulated green rings, and mushroom rings), and they are caused by fungi inhabiting soil and thatch. In this issue, we'll discuss the cause of Fairy Ring, and suggest some ways of dealing with it.

Pathogen: Marasmius oreades, Psalliota campestris and other mushroom species. The killing ring is more of a problem on the Prairies than in British Columbia.

Host Plants: All turfgrasses.

Season of Occurrence: Mushrooms are usually produced in the fall, but sometimes may occur in the spring. Other symptoms such as the killing ring or the stimulated ring may be visible at various times of the year.

Conditions Favouring Disease:

• There is more disease on sites with higher organic matter, such as in thatchy lawns.
• Long dry periods particularly during summer after a wet spring.
• Mushroom rings can occur on lawns or grass swards where tree stumps or other large pieces of woody organic matter have been buried.

Symptoms:

• There are 3 general types of fairy ring: 1) killing ring; 2) stimulated ring; and 3) ring or arc of mushrooms.
• The killing ring has been found in Europe in meadows and pastures to be kilometers in diameter and hundreds of years old. Dying turf at the edge of killings rings may have a purplish wilted appearance due to interference with root function. Advance of the ring will be halted when the fungus encounters obstructions such as trees, buildings, or even other rings, and this leads to arcs which grow outward. The interior of the ring recovers as the fungus grows outward giving a frog-eye appearance. There also may be enhanced growth just inside the dead ring or to the outside of the dead ring.
• The stimulated ring can achieve several meters in diameter. It is more prominent in areas of low nitrogen fertility. This is the most common type of fairy ring seen on creeping bentgrass putting greens. The rings may reappear in the same location year after year, and outward ring expansion is several mm per year. Symptoms can be masked by applying iron.
• The arc or ring of mushrooms can be found in areas of infrequent mowing. The fungus starts as a spore or mycelium growing on organic matter such as a buried stump. The fungus grows outward to colonize new organic matter, and during the degradation process, some nitrogen may be liberated that causes stimulation of turf growth. There may also be a dead zone due to mycelial growth preventing water penetration. In late summer and early fall, mushrooms may be produced at the margins of the ring.

Life Cycle: The fungus survives as mycelium in soil and thatch living off dead organic matter. One way to diagnose fairy ring is to slice into the affected turf and look to the presence of abundant white mycelium in the thatch and upper soil area. Mushrooms may be found in spring or fall that produce millions of spores. Cultural Control:

• Reduce thatch.
• Aerify to allow increased moisture penetration into soil.
• Irrigate excessively to cause saturated conditions for 4-6 weeks. This creates an environment which favours bacteria and other microbial antagonists.
• A drastic alternative is to remove infested soil and replace with new clean soil. Note that the fungal mycelium may be up to 0.5 m outside of the ring and as far down into the soil as the grass roots.
• Another alternative is to cultivate infested soil, which breaks up the fungal mycelium and allows competition. This is commonly done on home lawns on the Prairies, and after reseeding or resodding, problems were still not observed after 10 years.

Chemical Control: No registered fungicides in Canada for fairy ring. The ones registered on turf are not known to be effective. Soil fumigants will kill off the Fairy Ring fungus (but will kill many other things also).

Resistant Turfgrasses: None of the northern turfgrasses are resistant.

Dr. Tom Hsiang is the Turf Pathologist, Guelph Turfgrass Institute, University of Guelph

Turf Line News April/May 2000