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m y c o l o g i s t 2 0 ( 2 0 0 6 ) 36 – 37

Fungal foes in your garden: Fairy ring mushrooms

R. T. V. FOX

School of Plant Sciences, The University of Reading, 2 Earley Gate Reading, RG6 6AU, UK

1. The Disease

Thought by some to mark the tracks made by dancing fairies

(see Fig. 1), fairy rings can appear on lawns, golf courses or

other areas of turf during spring and summer. All grass spe-

cies and varieties are equally vulnerable. The usual symptom

is a ring of dormant, dead or dying turf closely encircled by

lush dark green grass. These concentric rings or arcs vary in

diameter from a few centimetres to more than 15 metres,

extending outwards each year by a few centimetres to over

a metre depending on the type of grass, soil and climatic con-

ditions. Multiple rings can form and grow into each other.

Hence fairy rings are more evident in poor soils and are larger

when the turf is suffering from moisture or nutritional stress.

Rings can suddenly disappear without apparent reason.

2. The Fungus

Although fruiting bodies may or may not be present, fairy

rings are caused by over 50 species of soil-inhabiting basidio-

mycete fungi, including the fairy ring fungus, Marasmius

oreades (Bolt.: Fr.) Fr., the common field mushroom, Agaricus

campestris L.: Fr.). (Syn. Psalliota campestris (L.: Fr.) Quel.) and

puffballs. In late summer and autumn the light tan-coloured

basidiocarp fruiting bodies of M. oreades can be found between

the bare and outer lush rings particularly after a period of

heavy rainfall or irrigation. In the absence of fruiting bodies,

a reliable diagnostic is to dig a few cm into the area of brown

or dead grass, to reveal the mouldy smelling, dense growth of

white mycelium. The rings start with the germination of basi-

diospores in the thatch layer. When basidiocarp samples of

M. oreades were studied by DNA amplification fingerprinting

(DAF) from carefully mapped fairy rings in a natural site,

the fungal population was found to contain many genotypes

and about 90 % of the fairy rings represented a separate genet.

This implied that establishment of new individuals generally

was mediated by basidiospore dispersal and not by fragment-

ing dikaryotic vegetative mycelium, as previously proposed.

0269-915X/$ – see front matter ª 2005 Published by Elsevier Ltd ondoi:10.1016/j.mycol.2005.11.013

However strands of mycelium might still be important inocula

in the garden. Previously considered an obligate saprophyte,

M. oreades is capable of parasitizing roots of grasses such as

Poa pratensis and Festuca rubra and produces hydrogen cya-

nide, polyacetylene and sesquiterpene metabolites capable

of damaging grass roots. The mycelium from each fairy ring

is a genetically homogenous entity that can be considered dis-

crete individuals as old as 100–150 y and possibly 500 y. The

fungus is heterothallic and has a unifactorial mating system

controlled by a multiallelic locus. As the fungus grows out-

wards in all directions a depth of 25 to 30 cm from a single

point in the thatch layer or on organic matter in the soil.

The first visible evidence of a new fairy ring is a tuft of dark

green grass. The ring of lush green growth is supported by sur-

plus nitrogen released by the fungal metabolism. If the soil

mycelium is abundant it interferes with the penetration of

water. The grass plants then suffer from drought and may

die, leading to the bare rings between the lush rings. As the

fairy ring expands the older part of the mycelium mat dies,

and grass or weeds can regrow in this older or center area.

Fairy ring fungi rarely grow back inside the ring after exhaust-

ing the original organic food source. Soil from the outer zone,

ring zone and inner zone of a fairy ring formed by M. oreades

on a garden lawn showed the amounts of soil organic C, total

N, microbial biomass C, and ergosterol were reduced by 46 to

54 % in the ring zone and by 25 to 37 % in the inner zone rela-

tive to the non-invaded outer zone. The water-to-soil organic

C ratio was markedly reduced only in the topmost horizon of

the ring zone. Ergosterol and microbial biomass C were very

closely correlated. An enhanced ergosterol-to-biomass C ratio

in the the ring zone clearly reflected the invasive growth of

M. oreades.

3. Control

Some non-mycologists regard fairy rings as unsightly but

since they are very difficult to control, most gardeners are

resigned to live with the problem. However before planting

behalf of The British Mycological Society.

Fungal foes in your garden 37

Fig. 1 – A Fairy ring caused by Maramius oreades showing the ring of bare soil (Photograph R. T. V. Fox).

a new area of grass or renovating an existing lawn, remove as

much organic matter as possible. Affected soil can be dug out

and replaced with new soil, although this is seldom practical.

Research on chemical drenches and biological control contin-

ues, but although fumigation of soil prior to reseeding has

been used with some success and some eradicant products

are already approved, chemicals are short-term solutions at

best. Fungicidal control, however, can be improved if a surfac-

tant is used to increase soil wettability. When fairy rings move

across or overlap each other, they will inhibit each other by

antagonism. This form of biological control can be manipulat-

ed if several fairy rings are present occupying the same site by

using a herbicide based on glyphosate to kill the turf over the

entire area, which is rotavated to mix the mycelium. After us-

ing a wetting agent to increase water infiltration to 20 cm, the

area is then re-turfed or re-seeded, kept adequately watered

and properly fertilized. Alternatively it has been shown that

the application of some mycorrhiza can be effective in restor-

ing unsightly scars as new grass overgrows the dead zones.

This regenerating biosphere should be well fertilized with or-

ganic fertilizer.

Keeping the fertility level of the turf high will also help to

mask the appearance of the rings of stimulated, dark green

growth. Grass should be fertilized with nitrogen several times

a year to help mask symptoms but as the infected soil

becomes virtually impervious to water, punch holes at least

every 30 cm in the yellowing or dying area and pump large

amounts of water into the ground to a depth of 25-60 cm. Re-

peat frequently. Increasing the soil moisture may also change

the ecological balance enough to retard the growth of the fungi.

Application of a wetting agent to the area may also increase

soil permeability and help to lessen symptoms. Aeration also

reduces the symptom severity. Regular mowing removes the

mushrooms, the other symptom of fairy ring disease.