Description of the Disease
Fairy ring is caused by a number of species of mushroom-forming fungi including many basidiomycetes in the order Agaricales. For example, Lepiota spp. are common in southern California, Marasmius oreades has been found in central and northern California, and Agrocybe pediades occurs in both southern and northern California. Many of these fungi are poisonous and must not be eaten.
Fairy rings are circular or semi-circular and can range in size from a few centimeters up to many meters in diameter. Symptoms can be variable, depending on the species of fungi, and include: 1) dark green rings with no dead turf; 2) dark green rings with a thin ring of dying or dead turf inside or outside the green ring; 3) rings of dying and dead turf with a hardened hydrophobic layer of soil that is difficult to irrigate; and 4) rings of mushrooms without a visible effect on the turf. Weeds commonly invade infested areas.
There are two types of fairy rings, edaphic (non-superficial) or lectophilic (superficial). Edaphic rings are generally formed by fungi that inhabit the soil underneath the turf. These frequently cause a hardened hydrophobic layer of soil above the areas of their active growth that prevents water penetration into the soil and often causes plant death. Rings of dead turf are frequently associated with this type.
Lectophilic rings are caused by fungi that inhabit the thatch layer and decomposed plant debris, litter, and old thatch. These rings are characterized by a slight depression of the affected areas surrounded by dark green rings of turfgrass where the fungi are breaking down plant material and releasing nitrogen. A hard, hydrophobic soil layer is not associated with this type of fairy ring.
The fungus survives as a white mass of mycelia in the soil or thatch layer, or can be spread by spores dispersed by the mushrooms produced by the rings. In some cases, rings or mushrooms can appear in the turfgrass and cause no apparent damage.
All grasses are susceptible to fairy ring.
Conditions Favoring Disease
A dense thatch layer contributes to the availability of undecomposed matter, as does the addition of composts or other organic material that have not been fully decomposed. Also, turfgrass growing in low fertility soils with insufficient irrigation appears to suffer more damage from fairy rings than turfgrass with adequate fertility and irrigation.
A turfgrass management program that provides proper fertilization and irrigation along with regular dethatching of the turfgrass will help prevent the development of this disease. Fungicide treatment or soil removal may be necessary if fairy ring becomes a problem.
To avoid or reduce symptoms, apply adequate nitrogen and water. Symptoms of superficial rings can be masked by nitrogen applications. If fairy rings are present, aeration followed by heavy watering for several weeks may help reduce symptoms; soil wetting agents may improve water penetration. Proper thatch management and regular dethatching can contribute to a reduction in the disease. Fairy ring can be eliminated by removing the turf and root zone with the soil containing the white, cottony, mycelial mass. If fairy ring symptoms consist only of mushrooms and there is no zone of dark green grass, the mushrooms can be raked off and disposed of. While this will not weaken or control the fungus, it will improve the turf's appearance.
Fungicide applications of azoxystrobin appear to provide good control of the disease when used properly. Flutolanil applications provide some suppression; control may be improved if applications are used in conjunction with cultural practices.
|Common name||Amount to use||Ag Use
|(Example trade name)||(hours)||(hours)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.|
|(Heritage)||0.4 oz/1000 sq ft||4||Until dry|
|MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)|
|(Prostar WG)||Label rates||12||Until dry|
|MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)|
|*||Permit required from county agricultural commissioner for purchase or use.|
|1||Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to a fungicide with a different mode-of-action group number.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production.|