Fairy Rings
There are known to be over 50 Basidiomycete fungi that can cause the development of fairy rings and the severity of the symptoms expressed on the turf will depend on the fungus that is causing the problem. These fungi will colonise either the base of the turf (superficial fairy rings or thatch fungi) or the rootzone and when colonising the rootzone, may result in a range of above-ground symptoms. We tend to refer to the most damaging rings as Type 1 and in these, the accumulation of fungal mycelium can eventually lead to areas of dying turf or bare ground that are bordered on both sides by stimulated turf growth and on their outer edge, may become colonised by fungal fruiting bodies (mushrooms / toadstools). Slightly less damaging to turf quality are the Type 2 rings where stimulated rings or arcs of turf may or may not be associated with fungal fruiting bodies and the least damaging of all are the Type 3 rings that show no change in turf quality but are visible only by the development of the mushrooms / toadstools. In all cases, removal of the immature fruiting bodies by mowing or brushing will help to limit further spread of the fungus.
Some fairy ring fungi can grow to several meters in depth in open, high sand content rootzones and here the symptoms on the over-lying turf can become extreme.
All of these fungi obtain nutrition from dead and decaying plant material and in breaking down the plant remains, the released nutrients are taken up by the fungus for its growth. Some nutrient will also be taken up by the turf roots and this results in some of the stimulated plant growth. The developing fungus grows radially outwards from a central point, increasing in mass as it does so. The old fungal mycelium towards the centre of the rings will eventually die and release nutrient back in to the soil. This release of fungal cell contents is also responsible in part for the stimulated
plant growth.
The fairy ring fungi will cease growth only if they run out of nutrient on which to feed, a solid barrier or disturbed ground. If two rings grow in to one another, they ‘mutually inhibit’ each other’s growth and a figure of eight will develop. If similar growth continues to occur,
arcs and ribbons of fairy rings will develop.
One of the main problems with fairy ring growth is the development of water-repellent soil and this can result in the turf being unable to access water and nutrient. Management of fairy rings is strongly aligned to managing rootzone repellence. The sward in fairy ring affected areas can often develop foliar fungal diseases including Microdochium Patch, Red Thread and Anthracnose Foliar Blight as a result of the stimulated plant growth or water related stress that is associated with different phases of fairy ring development.
Management of fairy ring symptoms includes being aware of the depth of fungal infection through the rootzone. Rootzone core samples taken to depth can be used to determine the depth of water-repellence through the profile and any applied wetting agent (surfactant) will need to be watered in sufficiently to penetrate the affected depth. Often, wetting agents will need to be routinely re-applied to affected areas and the initial application should be made prior to the rootzone becoming dry. Any applied fungicide with labelled efficacy against fairy rings will need to be positioned sufficiently deep in the profile as to reach the fungal mycelium. Due to the observed mutual inhibition of fairy rings, there is a possibility that removal of the turf and rotovation of the affected rootzone could lead to the fungus effectively killing itself out. There is always the possibility that this approach will result in the occurrence of an increased number of small rings so care should be taken before this is considered!