MTC Turf News – Peter H. Dernoeden, Ph.D – Professor Emeritus, University of Maryland

The cause of fairy rings was the subject of much folklore in Europe in Medieval times. Most agreed that the rings likely were caused by elves dancing in rings, but Germans thought they were burned into the ground by dancing witches (Hexenringe). Entering a ring could result in very bad luck, including loss of an eye or even crumbling into dust; this was especially true on Halloween. Children could avoid trouble after entering a ring, by running around the ring nine times; ten times could put you into much more trouble. More scientifically oriented nineteenth century Americans attributed the rings to the activities of ants or snails or perhaps lightning. Shantz and Piemeisel, excavating fairy rings in Eastern Colorado in 1917, were the first to suggest that fairy rings killed vegetation by rendering infested soil impermeable to water. Even today, the presence of fairy rings conjures interest and mystery, until they start killing your grass (Photo 1).

Fairy rings are commonly found in turf and pastures and may be caused by 50 or more species of fungi.  Fairy ring fungi belong to a group known as the basidiomycetes or “mushroom fungi,” which includes puffballs. Among the more common mushrooms associated with fairy ring are Agaricus spp, which are closely related to the fresh-white mushrooms you buy in the grocery store. Lycoperdon spp. and Vascellum sp. (known as puffballs) are the primary cause of fairy rings on golf greens. There are many other basidiomycetes commonly found around homes, golf courses, mulched and wooded areas, including bract/polypores (major wood rotter’s); birds nest, club, toothed, earthstars morels, stinkhorns, jelly fungi and artillery fungi. The basidiomycetes play a major role in nature through their ability to degrade organic matter. In particular, they break-down the toughest type of plant organic matter called lignin. Lignin is the strengthening material in cell walls and it occurs in its largest amounts in wood (Photo 2).

Most of the fungal body (a network of filaments called mycelium) of a fairy ring resides in thatch and below ground. At some point in time, usually beginning with warmer rainy weather in spring, these fungi produce above ground, spore producing fruiting bodies (i.e., basidiocarps = mushrooms and puffballs). The entire reproductive process remains a mystery to this day; specifically, how can a mass of mycelium in soil transform itself to produce elaborate, fleshy above ground reproductive structures? The typical mushroom has a cap and stem. The underside of the mushroom cap is composed of gills, upon which spores are produced. Puffballs do not produce caps and spores are borne within white, fleshy and egg-shaped fruiting bodies. Puffballs often have fleshy warts or spines on their surfaces. Mushrooms and puffballs turn brown as they age, and when they crack or are crushed they release large numbers of spores. Spore color is helpful in identifying basidiomycetes; they can be white, yellow-brown, pink, purple-brown or black. Spores or transport of infested soil spread fairy ring fungi, but it remains a total mystery how a single spore or fragment of mycelium can give rise to perfect green circles or sickle-shaped arcs in turf. Somehow, the fungus initiates growth at a central point (via spores or mycelial fragments) and continues outward in all directions (i.e., radial) at an equal rate (Photos 3, 4, 5, 6).

The presence of fairy rings can remain evident all year, especially in lawns. It is not unusual for rings to disappear and then reappear at a later time. They are more notable and numerous in wet years but are most destructive when weather conditions become hot and dry. Fairy rings are among the most destructive turf diseases, but they are not pathogens. Some species do form symbiotic mycorrhizal relationships; this symbiosis is largely associated with trees.

Fairy ring fungi cause the formation of rings or arcs of dead or unthrifty turf, or rings or arcs of dark-green, luxuriantly growing grass. Fairy rings are classified into three types according to their effects on turf:  Type 1 Those that kill or badly damage plants in rings or arcs. Type 2 Those that stimulate grass, causing the formation of rings or arcs of dark green turf. Type 3 Those that do not stimulate grass and cause no damage, but produce fruiting bodies (i.e., mushrooms or puffballs) in rings or arcs.

Fairy rings vary in size from 1 to 20 feet or more in diameter and become larger each year. Indeed, in parts of Europe, rings as great as 2000 ft. in diameter have been observed in pastures and are believed to be over 100 years old. Rate of outward movement, as well as overall ring diameter, is determined by soil and weather conditions. In general, rings grow more rapidly in light-textured (i.e., sandy loams) and moist soils than in heavy clay and dry soils. Rings fade in the autumn or winter, but bare zones remain visible until turf recovers via stolons, rhizomes and/or tillering. Fairy rings are most conspicuous during hot and dry summer periods, but can fade rapidly with the advent of rainy weather. When soil moisture is abundant, dark green arcs or rings may be evident, while the dead zone is absent. With the advent of warm to hot and dry weather, however, the dead zone appears.

The most destructive rings are of the Type 1 variety. Type 1 rings are very common in lawns and on golf courses. In lawns, roughs and fairways, Type 1 rings initially appear as circles or arcs of dark-green grass, but the dead zone does not appear until dry periods in summer. Classic Type 1 rings are distinguished by three distinct zones: an inner lush zone where the grass is darker green and grows luxuriantly; a middle zone where the grass may be wilted or dead; and an outer zone in which the grass is slightly (i.e., less lush vs inner green zone) stimulated and/or darker green. The distance from inside of the inner zone to outside of the outer zone may range from a few inches to a foot or more wide. The distinct double green zones, with a dead zone are uncommon on golf greens. On greens, a single green zone usually develops first, which may or may not wilt and develop a dead zone (Photo 7).

Darker green, stimulated zones classic to higher cut lawns and roughs are the result of the breakdown of organic matter, which releases nitrogen and results in more vigorous leaf growth. The outer green zone is caused by the breakdown of thatch and organic matter by the fairy ring fungus, which liberates nitrogen.  The inner green zone, which is wider and more prominently dark green, develops in response to the release of nitrogen as bacteria and other microbes degrade aging or dead mycelium of the fairy ring fungus. Mushrooms or puffballs are produced at the junction of the bare and outer green zones. Rings, however, may produce few or no mushrooms, especially on golf greens (Photo 8, 8a, 9)

Type 2 fairy rings are commonplace and can appear in early spring and remain evident until winter. Type 2 rings tend to come and go, but are most prevalent during wet summer periods. Type 2 fairy ring can develop into a Type 1 fairy ring during hot and dry periods. Fruiting bodies develop within the darker green zone following rainy weather in summer. Type 3 rings of mushrooms or puffballs growing in a ring or arc are mostly found in infrequently mowed fields and lawns, and usually appear rapidly after a rainy period. Classic Type 3 rings generally do not develop a stimulated green zone (Photo 10, 10a, 11, 12).

In lawns, roughs and pastures, a fairy ring is broken when its mycelium encounters an obstacle such as a rock, pathway or unfavorable soil condition. In general, two fairy rings will not cross one another; that is, at the point of intersection the growth of each ring stops. This obliteration at the point of contact is caused by the production of self-inhibitory substances, which also antagonize other members of the same or different microbial species. On slopes, the bottom of a ring usually is open, giving the appearance of an arc or crescent. This may be due to the downward movement of self-inhibitory metabolites that prevent development of fungal mycelium on the lower side of the ring (Photo 13).

When a plug of soil is removed from the edge of an active fairy ring, a white thread-like network of mycelium sometimes may be seen in the thatch layer or clinging to soil and/or roots. When environmental conditions are optimum for fungal growth, white mycelium may be seen on the surface of the thatch layer. Oftentimes, however, no mycelium is evident in the soil or thatch. Fairy ring infested soils, however, invariably have a mushroom odor, even if fungal mycelium is not evident. In all turfs, to include greens, thatch layers in active rings are light-brown or fawn-colored rather than the more normal dark-brown color (Photos 14,15,16).

Type 1 fairy ring fungi kill turf primarily by rendering infested soil impermeable to water (i.e., hydrophobic) and plants die from drought. It is quite characteristic for grass on the outer edge of the dead zone to initially display the blue-gray color of wilt before dying. Very high concentrations of ammonium have been measured (Dr. Mike Fidanza, UM Ph.D.) in the wilting zone of Type 1 fairy rings, and levels can be toxic enough to cause turf death. This is most notable during rainy periods following a nitrogen fertilizer application. The rapid release of ammonium via the degradation activities of fairy ring fungi causes is a brilliant flaring at the outer periphery of the ring. Some fairy ring fungi are known to produce compounds toxic to roots such as hydrogen cyanide. It is likely, however, that most damage to turf can be attributed to the fungal mycelium (either by its physical presence or as a result of organic “hydrophobic” compounds released as older/dead mycelium is degraded by microbes) rendering soil hydrophobic. The resulting hydrophobic conditions render soil impervious to water penetration (i.e., rain water runs-off) and dead zone plants simply die of drought. Probing will reveal that soil in the dead zone is bone-dry (Photo 17).

ProStar (flutolanil) was the first fungicide labelled for control of fairy ring. Over time, it was shown that DMI/SI fungicides (e.g., Bayleton [triadimifon]; Mirage/Torque [tebuconazole]; Tourney [metaconazole]; Trinity [triticonazole]; others {note Banner MAXX; propiconazole is not labelled for fairy ring control}; strobilurins (Heritage [azoxystrobin]; Insignia [pyraclostrobin]; others); Affirm/Endorse [polyoxin D]; and Velista [penthiopyrad] also are effective.

Research has shown that it is not necessary to core prior to applying fungicides targeting fairy rings preventively on golf greens. It is important to note that most successful fairy ring fungicide programs begin in spring with the routine use of soil wettings, prior to the appearance of fairy ring activity. Good fairy ring suppression has been reported by applying an appropriate fungicide in a high water volume (i.e., ≥100 gal. water/acre) or by simply watering it off foliage. This may be because puffball fairy ring fungi common in golf greens grow closer to the surface. The depth of fungal growth is difficult to estimate. One way to check is to collect a cup cutter or profile sampler plug from within an active (green, not dead area) ring. Moisten the soil and place the sample in a plastic bag and incubate at a warm (> 75ºF;) temperature. Mycelium may be evident within 24 to 48 hours, thus giving an indication of the depth of fungal growth and therefore the depth to which a fungicide should be watered-in.

Steven McDonald (MSc. from UM: Pres. Turf. Dis. Solns.), has observed effective fairy ring suppression/control in sand-based golf greens, as well as tees and fairways grown on native soils, using a DMI/SI in spring. Fungicides should be applied twice about a month apart once soils warm to about 65F for 4 or 5 days (normally May) and again in June. Steve cautions that some DMIs can have a negative growth suppression and/or discoloration effect (i.e., stunting and a blue-gray discoloration response). Similar results can be achieved by rotating in one of the other aforementioned (non-DMI/SI) fungicides. As I have observed over the decades, different chemistries can work differently for different golf courses. Most superintendents need to do their own on-site testing to find those chemicals that work best on their golf course.

As noted above, effective fairy ring control in greens is dependent on being on a routine soil wetting agent program by mid-May. If green rings appear in the absence of a wetting agent program, it now becomes essential to include a wetting agent combined with coring in a curative program involving fungicides. Wetting agents aid water infiltration by breaking the surface tension of hydrophobic soil. This method of control involves a combination of core or solid tine aeration, deep watering, and use of soil wetting agents. Aeration is beneficial since it opens surfaces and aids in the penetration of air and water.  The entire area occupied by the ring, to include a two-foot periphery beyond the ring, should be cored on 2.0 to 4.0 inch centers. The area should be treated with a soil wetting agent plus an effective fungicide, and then irrigated so that water penetrates to a depth below the hydrophobic zone (about 4.0 to 6.0 inches in depth). It should be noted, that tank-mixing a DMI/SI fungicide with a wetting agent can result in enhanced discoloration or even a phytotoxic response. Hence, an alternative fungicide (e.g., Affirm, Heritage, Insignia, ProStar, etc.) noted above, could be recommended when curatively mixing a fungicide with a soil wetting agent. The role of the wetting agent is to facilitate entry and percolation, but caution is needed to ensure chemical is not moved below the effective zone. Follow-up applications of fungicides likely will be needed on two- to four-week intervals until “ring wilting” no longer occurs. The ring area should be re-treated in a similar fashion at the earliest indication of drought stress; that is, repeat the process whenever the dark-green grass turns blue-gray and begins to wilt. Even using a pitchfork to create openings is preferred to not creating any holes at all.

For lawns, the old idea of using wetting agents and injecting water into wilted areas does not work. In my own experience, I have found that drenching a fairy ring in spring with a DMI (e.g., Bayleton and others) before there is any wilt works really well. The procedure simply involves mixing a few ounces of fungicide and liquid soap (e.g., Joy) in a bucket of water and drenching the outer perimeter of the ring. Homeowners will need work with an LCO to get the job done properly.

Mushrooms are beautiful gifts from Nature and serve many beneficial purposes. Most importantly, these fungi are major contributors to the breakdown of dead organic matter. Along with other microbes, the basidiomycetes slowly and inexorably degrade wood lignin and remove all traces of dead plant life and return it to soil. Some mushrooms are edible and delicious. Some can give a belly ache or even kill you. Others, upon consumption, can send you on a magical mystery tour. Unfortunately, botanical taxonomists are no longer trained or available to identify mushrooms or any other forms of unusual plant life. Their demise is the direct result of our Land Grant Agricultural University System to give way to molecular biology to solve all unknowns. Bottom line; never eat mushrooms gathered from outdoors (Photo 18).

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