Fairy ring is considered one of the most common turfgrass diseases globally, and over 60 species of basidiomycetes are known to cause fairy ring symptoms in turf, making it one of the most common turfgrass diseases globally (Couch, 1995; Smiley et al., 2005; Smith et al., 1989). Fairy ring symptoms observed in a turfgrass stand are the result of a complex interaction between the basidiomycete-causing fungus and the soil root zone and turfgrass thatch (Fidanza, 2015, 2007b; Fidanza et al., 2007). The medieval period is filled with folklore and strange tales of mushrooms magically appearing overnight in a circle (i.e., “fairy ring” since the cause was attributed to mythical fairies or “faeries”) in pastures and woodlands (Wiggen and Smith, 2000), but the first scientific investigation into the soil chemistry of fairy ring-affected sites was published in 1807 (Wollaston, 1807). In 1917, Shantz and Piemeisel published their results of observing fairy ring sites in the grasslands of eastern Colorado, and developed a system to visually describe fairy ring symptoms in nature labeled as Type I, Type II, and Type III. This same fairy ring scale or categorical description was reintroduced and reemphasized in recent publications (Couch, 1995; Fidanza, 2009, 2015; Smith et al., 1989).
Type I fairy ring symptoms are characterized by dead turfgrass appearing in a peculiar geometric pattern of rings or semicircles or arcs (Fig. 1), as the result of a complex interaction of the basidiomycete fungus and the soil root zone and thatch (Couch, 1995; Fidanza, 2007a, 2007b; Fidanza et al., 2007; Shantz and Piemeisel, 1917; Smith et al., 1989). Type II symptoms are indicated by the visual appearance of darker green, stimulated, and lush-growing turf, also in a pattern of rings or semicircles or arcs, compared with the surrounding healthy turf (Fig. 2). Turf affected with Type II symptoms reveal a growth response similar to a dose of soluble nitrogen fertilizer (Fidanza, 2009; Fidanza et al., 2007; Smiley et al., 2005). Type II visual symptoms typically would be considered more visually acceptable compared with Type I symptoms (Fidanza, 2015). Type III symptoms (Fig. 3) are the visual appearance of basidiocarps (i.e., mushrooms or “toadstools” or “puffballs”), which represent the fruiting body or spore producing stage of the fungus (Shantz and Piemeisel, 1917). The mushrooms are often seen literally “popping-up” overnight after a heavy rain event. In turf, these visual fairy ring symptoms or “types” can occur alone (Figs. 1–3) or together (Fig. 4) in various combinations.
In research, typical turfgrass disease rating strategies do not work as well for fairy ring (Fidanza and Settle, 2013; Fidanza et al., 2003, 2005). For example, dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in turf is often rated by visually counting the number of active infection centers or foci per plot, which may work fine for counting individual mushrooms or puffballs, but not an area of wilted, necrotic, or dead turf within a test plot. Rhizoctonia blight or brown patch (Rhizoctonia solani Kühns) in turf usually is evaluated in test plots by estimating the percent plot area blighted. With fairy ring, a percent plot area blight rating may not reveal the correct interpretation of fairy ring activity or turfgrass injury (Fig. 5). For example, at first glance it may seem that a 5 × 5 ft (1.5 × 1.5 m) test plot with 50% plot area affected by dark green, stimulated turf in an arc or small circle (i.e., Type II fairy ring symptoms) would be more severe compared with another test plot that had 10% plot area affected with necrotic and dead turf in a small semicircle (i.e., Type I). In reality and in terms of judging the complex threat of fairy ring symptoms in turf, a 10% plot area of necrotic or dead turf would be considered much more severe and troublesome and difficult to manage vs. 50% plot area of dark green, stimulated turf (Fidanza, 2009; Fidanza and Settle, 2013). Of course, the diameter of actual fairy ring symptoms in turf can vary from a few inches (cm) to several feet (m) (Smith et al., 1989). Also, it is extremely difficult to visually estimate the actual percent plot area displaying fairy ring symptoms. For example, does one measure the entire circular area of a fairy ring, or, measure only the specific dark green perimeter area of the circle (Fig. 5)? Therefore, over the past several years with conducting fairy ring trials and field studies in turf, it has become evident that a better rating system was needed. The goal of this project was to develop a “Fairy Ring Severity Index” to help quantify and categorize visual fairy ring symptoms in turf.
CampbellC.L.MaddenL.V.1990Introduction to plant disease epidemiology. Wiley-Interscience New York NY
CouchH.B.1995Diseases of turfgrasses. 3rd ed. Krieger Publishing Malabar FL
FidanzaM.SettleD.2013Evaluation of an inorganic soil amendment to reduce and manage fairy ring symptoms in turfgrassUSGA Turfgrass Environmental Res. Online12368
FidanzaM.A.SanfordD.L.WetzelH.JrNattleJ.S.2003Evaluation of fungicides a soil wetting agent and cultural practices for curative fairy ring control 2001. Fungicide and Nematicide Tests 58:T036
FidanzaM.A.CisarJ.L.KostkaS.J.GregosJ.S.SchlossbergM.J.FranklinM.2007Preliminary investigation of soil chemical and physical properties associated with type-I fairy ring symptoms in turfgrassHydrol. Processes2122852290
FidanzaM.A.ColbaughP.F.EngelkeM.C.DavisS.D.KenworthyK.E.2005Use of high-pressure injection to alleviate type-I fairy ring symptoms in turfgrassHortTechnology15169172
MeadR.CurnowR.N.HastedA.M.2003Statistical methods in agriculture and experimental biology. 3rd ed. Chapman and Hall/CRC Boca Raton FL
SettleD.FidanzaM.2007Fairy ring research. On Course. J. Midwest Assn. Golf Course Superintendents 61(3):11–15
SmileyR.W.DernoedenP.H.ClarkB.B.2005Compendium of turfgrass diseases. 3rd ed. APS Press Minneapolis MN
SmithJ.D.JacksonN.WoolhouseA.R.1989Fungal diseases of amenity turf grasses. E & F.N. Spon Ltd London UK
WiggenK.D.SmithN.A.2000The fairy ring: Favorite fairy tales of many countries. Reprinted from 1910 edition. Fredonia Books Amsterdam The Netherlands