Plant Disease of the Week No. 9d (Fairy rings)

Disease name: Menehune rings, fairy rings

An arc of Chlorophyllum molybdites, the Green-spored Parasol, on a residential lawn

Fairy ring symptoms: Continuous circles or arcs, formed by bands of turfgrass that are darker green and more quickly growing than adjacent grass plants of the same species. This band, the "stimulated zone" of grass, may range in width from several inches to about one foot. Rings tend to occur together in the same area. Rings may overlap, creating scalloped edges where the leading edges of adjacent exterminate each other. Ring diameter may range from a meter (a few feet) to 20 meters or more.

Note on age of fairy rings: According to the British researcher Dickinson (1979), the radial growth rate of grassland fairy rings was measured between 99 and 350 mm/year. Diameters up to hundreds of meters were recorded. Therefore, fairy rings may be among the world's oldest living organisms. Many rings may centuries old and some might be 600 or 700 years old.

Fairy ring signs: When soil moisture is high, fungal fruiting bodies of the pathogen may grow in and along the circular band of stimulated grass. Common names for these sporophores include mushrooms, toadstools and puffballs. They can be abundant and can form a continuous circle throughout the circumference of the rings.

Photos: (above right) A partial fairy ring in a residential lawn in Holualoa, Hawaii. The partial ring of mushrooms (Chlorophyllum molybdites, the Green-spored Parasol) appeared after several days of heavy rainfall. The underground body of a fairy ring fungus consists of a network of filaments, the mycelium. It grows radially outwards as it decomposes and feeds upon organic matter in the soil. Behind the advancing fungus front, the mass of mycelium dies. The dead mycelium forms a dense and water-repellant mat that causes grass to die from drought stress. The green ring developed as the fungus grew through the soil and thatch, decomposing organic matter. This decomposition of organic matter releases ammonium. Other microorganisms reduce the ammonium to nitrate, and the nitrate stimulates lush growth of turf ahead of the leading edge of the fairy ring. The green outer band of lush turf normally coincides with a ring of toadstools (lower right) (photo - S. Nelson, UH-CTAHR).

Hosts (common name):
turfgrasses

of all types

Hosts (scientific name):

all commonly cultivated turfgrasses

Pathogens: More than 50 species of basidiomycete fungi. Some species are edible, some are deadly poisonous. Genera of basidiomycetes associated with fairy rings include Agaricus, Agrocybe, Amanita, Boletus, Bovistra, Calvatia, Cantherellus, Chlorophyllum, Clitocybe, Collybia, Cortinarius, Disciseda, Hebeloma, Hydnum, Hygrophorus, Lactarius, Lepiota, Lycoperdon, Marasmius, Paxillus, Scleroderma, Tricholoma, and Vascellum. Photo: Chlorophyllum molybdites, the Green-spored Parasol mushroom, a poisonous species infesting a residential lawn in Holualoa, Hawaii (photo - S. Nelson, UH-CTAHR).

Classification of the pathogens: Fairy-ring pathogens are basiodiomycetes, fungi that produce their sexual spores (basidiospores) on club-shaped spore-bearing structure (basidium). Most basidiomycetes are fleshy fungi (i.e., mushrooms, puffballs, stinkhorns, conks) involved in wood decay or as pathogens of higher plants, causing root and stem rots of trees.

Geographic range of pathogens: worldwide

Geographic range of pathogens in Hawaii: statewide

Host range of pathogens: The fleshy-fungi basidiomycetes exist saprophytically on decaying organic matter, while some species also have a parasitic phase on higher plants, causing root rots and stem rots of trees. Some non-fleshy species of basidiomycete fungi cause devastating diseases worldwide: the rusts and the smuts.

Disease etiology: Two types of disease manifestations are of concern with fairy rings. One, grass plants either green up unacceptably due to excess nitrate availability, or secondly, the plants wither and die from drought stress brought about by fungus-induced soil hydrophobicity.

Basidiomycete life cycle: The fairy ring fungus remains in a mycelial, vegetative growth mode most of the time, and this is how its body expands in the soil or thatch. The mycelium explores the soil depths and also laterally, breaking down organic matter and absorbing nutrients. Sexual reproduction and sporophore production occur only during favoring environments, usually wet. The mushrooms, or other types of sporophores, appear in Hawaii after at least several days of rain in lawns or landscapes, or at any time after frequent and thorough watering on golf courses or other sports turfs. After a week or more of continuous rainfall, fairy rings become a common sight in landscapes throughout Hawaii. The fruiting bodies bear the tiny basidiospores for long-distance dispersal of the fungus by wind, water or through incidental contact with and transport by a vector. Eventually some of these spores create new infections in turfgrass elsewhere, renewing the disease and life cycles.

For well illustrated introductory information about basidiomycete life cycles and the life cycles of mushrooms, please visit Dr. George Wong's (UH Manoa, Botany) websites on these topics for Botany 201:

Basidiomycete life cycle: http://www.botany.hawaii.edu/faculty/wong/Bot201/Basidiomycota/Basidiomycetes.htm

Mushroom life cycles: http://www.botany.hawaii.edu/faculty/wong/Bot201/Basidiomycota/Mushroom_Lifecycle.htm

Summary of the fairy ring disease cycle: Small, green rings appear as the initial symptom of the infection. The rings become progressively larger over time and the fungus grows radially in the thatch and/or the soil. The rings can increase in size up to about 0.5 m annually and can become quite large after years of infection have ensued. Some of the largest and oldest organisms on Earth are the subterranean fungi such as fairy rings.

Dissemination - basidiospores or mycelial fragments are dispersed by wind, water, soil or on tools and equipment.
Inoculation - basidiospores or mycelial fragments are deposited in thatch or soil containing the appropriate type of organic matter for a food supply (decaying wood or grass clippings).
Infection and pathogen development - the basidiospore(s) or hyphal fragment(s) germinate within the thatch or soil and begin to grow outward in all directions. The fungus withdraws nutrients from the organic matter in the soil. The fungal mycelium spreads throughout the thatch or soil layer, up to 12 inches deep in some soils.
Symptom and disease development - the first evidence of infection is the presence of a cluster of mushrooms or a band or tuft of dark green grass. The ring or band of green grass results from the nitrogen that becomes available as the fungus decomposes the organic matter in the thatch or soil. A central area or spot or ring of dead grass may develop, caused by a loss of soil moisture from the area of fungal concentration. In the hydrophobic layer of dead grass and contaminated soil is a thick growth of fungal mycelium.
Reproduction - Sexual reproduction occurs and mushrooms or other sporophores form at the periphery of the rings during periods of favorable conditions (rainy weather or intensive irrigation). The basidiospores are borne in the gills of mushrooms.
Survival - the fungi survive as spores and mycelial fragments in or on organic debris, and as pathogens of woody plants (roots, stems).

Pathogen dispersal: wind, rain, vectors (insects, slugs, snails, etc.) or human-assisted (via movement of infested or infected materials such as seed or tools).

Environmental conditions favoring disease development: warm, moist, wet soils, followed by very dry periods.

Predisposing factors:

Buried wood in the landscape (tree logs, limbs, roots, construction lumber, etc)

Stressed or under-nourished turf

Excessive irrigation

Heavy or unmanaged thatch

Poor soil aeration

Inadequate or poor soil layer beneath the turf

Other ring-like turf problems: Other turf diseases create ring patterns in turf, but are not caused by basidiomycetes and they are not classified as fairy rings.

Integrated pest management practices (IPM) for fairy rings:

It is important to identify the fungus associated with a fairy ring to genus level in order to achieve the best control, because the available fungicides may vary in their ability to suppress certain species. Accurate identification can only be done by collecting the sporophores of the pathogen.

Avoidance of fairy rings:

When building a golf course or installing new turf, ensure that no buried lumber or wood remains in the soil, such as tree stumps and roots. Do not use bulldozed trees as fill materials in the landscape.
Use caution when treating existing fairy rings not to move infested soil to new locations.
Minimize plant stress; this may mean raising the mowing height on fairways, tee boxes or greens while treating fairy rings.
Maintain optimum growing conditions for turfgrass with proper irrigation, thatch control, and fertility.
Vertical mowing to remove thatch, followed by topdressing.
Remove tree stumps and roots from existing turf installations.
Avoid excessive applications of irrigation water and fertilizers, because these practices favor the formation and growth of fairy rings .
Fungicide applications used as preventive measure may help.

Suppression of fairy rings:

Suppress mycelial growth with fungicides applied either as a drench or locally via syringe. Before selecting a fungicide, the basidiomycete fungus should be accurately identified. See "Fungicidal Suppression of fairy rings" below.
Mask the symptoms or signs - (1) aerate the soil and drench it with a wetting agent to help retard the development of zones of dying and dead grass; (2) fertilizers can mask the appearance of the "stimulated zone" of dark green grass, use additional N (about 0.1 to 2.5 lb per 1000 square feet) in the area where rings occur to mask the dark green bands of turf; (3) if the fairy rings consists of only sporophores with no stimulated zone of green grass growth, rake off and dispose of the sporophores (wash hands and tools when finished).

Eradication of fairy rings:

Dig out the fungal mycelium from the soil and remove it; this is more feasible for smaller-sized rings that are few in number. Remove and destroy the sod or kill it with a non-selective herbicide - do not compost it. A soil fumigant such as metam-sodium (Vapam) may be used to eradicate the residual fungal mycelium from the soil. It may be necessary to remove the soil to a depth of almost 3 feet, depending on the ring. The hole should be filled with clean or sterile soil or plant growth medium and re-seeded.

Fungicidal suppression of fairy rings:

Fungicides may be used to suppress fairy rings before or after they become established, although the efficacy of the treatment may be poor and dependent upon the basidiomycete species, the turf, and the environment. It is difficult to eradicate severe fairy rings infestations with fungicides alone. The best course for most home owners is to mask the fairy ring symptoms with fertilizers, rather than by applying fungicides. High-value turfgrass installations will use fungicides routinely as preventive and curative measures. The fungicides vary in their efficacy, formulations and methods of application.

Some fungicides for sale in Hawaii for control of fairy rings on turfgrasses.*

Product name**	Active ingredient	Formulation
Bayleton (various products)	Triadimephon (50%)	Wettable powder
Disarm 480 SC	*1	Flowable concentrate
Endorse (various products)	Polyoxin D zinc salt (2.5%)	Wettable powder
Headway	Propiconazole (9.45%); Azoxystrobin (5.73%)	Emulsifiable concentrate
Heritage TL	Azoxystrobin (8.8%)	Emulsifiable concentrate
Heritage	Azoxystrobin (50%)	Water dispersible granules
ProStar 70WP	Flutalonil (70%)	Wettable powder

*1 Methanone, [2-[[6-(2-chlorophenoxy)-5-fluoro-4-pyrimidinyl]oxy]phenyl](5,6-dihydro-1,4,2-dioxazin-3-yl)-, O-methyloxime)

* soil sterilants methyl bromide and metam-sodium are also available for certain applications

**arbitrarily selected product names, others may be available.

How to apply fungicides for fairy ring suppression:

First, the entire diseased are should be aerated at least every 4 inches. In addition, an area extending about 2 feet out from the edge of the fairy ring should be aerated and treated with fungicide. After aeration, clean the equipment with appropriate sterilizing agent(s) to disinfest. The area is soaked with water by hand (containing a wetting agent) after aeration

Example - flutalonil (the text below appears on the PROSTAR 70WP label). Flutalonil is regarded as the turf industry standard for suppressing most fairy rings.

a) Preventative: "PROSTAR 70WP Fungicide, applied in 10-50 gallons of water at 2.2 oz. per 1000 square feet, may suppress the development of fairy ring caused by various basidiomycete pathogens. A second application may be made at a 21- to 28-day interval using the same dosage rate."

b) Curative: "PROSTAR 70WP Fungicide, applied in 10 to 50 gallons of water at 4.5 oz. per 1000 square feet, may suppress the development of fairy ring caused by various basidiomycete pathogens. Application should be made to the affected area at the first sign of ring development (greening, death of turf, mushrooms). Symptom suppression may be temporary and symptoms may reoccur. In these cases, a second application at 4.5 oz. per 1000 square feet is suggested, not less than 30 days after the first application. Aerification prior to subsurface applications has been beneficial in some cases. Use of a nonionic surfactant in combination with PROSTAR 70WP is recommended. Treated areas should be irrigated prior to and after application with sufficient water to maintain growth of turf. Disease control is improved if turf is maintained at optimum fertility levels after symptom development. Turf that has been damaged extensively by fairy ring development may have to be reseeded. Do not treat more than 10,000 square feet per acre of turf area."