Conquering fairy ring disease with new tools

Hiding the rings with heavy fertilization is not the only option.

Michael A. Fidanza, Ph.D.

Types of fairy ring fungi Types of fairy ring fungi by region

Dozens of fungi cause fairy ring in turf. New fungicide technologies promise better preventive and curative control of fairy ring. New fungicide technologies promise better preventive and curative control of fairy ring. Fairy rings can kill turf by creating a water-repellent and droughty soil, by depriving the turf of nutrients or by releasing toxic substances.

Fairy ring disease occurs worldwide on greens, fairways, tees and roughs (2). Disease symptoms appear as widening rings or arcs in the turf that stand out because they are either dead or unhealthy, or green and actively growing. Circular patterns of mushrooms are also common.

More than 60 species of basidiomycete-type fungi (1,5,6) can individually cause the disease. These mushroom fungi primarily colonize thatch, mat and organic matter. The green rings are the result of nitrogen released in the soil by the fairy ring fungi's activities underground, where they break down organic matter to release ammonia, which is processed by soil microorganisms into nitrates (1,7).

Widening rings and arcs of dead turf reveal the presence of fairy ring fungi in this bermudagrass green.

Although fairy rings can kill turf, they often receive little or no treatment because only radical and costly actions such as fumigation or excavation of soil proved effective for many decades. The most popular "cure" called for masking symptoms with fertilizers and irrigation to make all the turf as green as the fairy rings.

Today, several control strategies, including fungicide applications, are available.

Fungicide treatment
Turfgrass death from fairy ring occurs when the fungal mycelia accumulate in the soil, coating sand and soil particles with a hydrophobic material. As the soil becomes water repellent, turfgrass plants are injured or killed by drought symptoms. The dried-out soil is then difficult to re-wet. In addition, some fairy rings may kill turf by releasing toxic compounds or depleting available nitrogen (1). Fairy rings, whether edaphic or lectophilic, can range in size from a few inches to several feet in diameter.

Recent advances in turfgrass research have made it possible for golf course superintendents to manage fairy ring with preventive as well as curative approaches.

One example of a preventive fairy ring strategy occurred at Sun 'N Lake Country Club in Sebring, Fla. (3). After the golf course rebuilt nine greens during the spring of 1995, severe fairy ring injury was observed the following spring. The club wanted to prevent fairy ring from becoming a serious problem on the nine holes remaining to be rebuilt. Superintendent Mark Hopkins, a 10-year member of GCSAA, worked on the problem with the club membership; University of Florida turf pathologist Monica Elliott, Ph.D.; and AgrEvo USA Co.

The untreated Tifdwarf bermudagrass in the foreground is heavily infested with fairy ring, but in the background the fungicide-treated half of the newly constructed green has no fairy ring.

The nine additional greens were rebuilt during the spring of 1996. A 12-inch-deep layer of root zone was cut out of the existing greens and was replaced with an 85:15 mix of sand and Canadian peat. The nine rebuilt greens were sprigged in May 1996 with Tifdwarf bermudagrass (Cynodon hybrid). In November 1996, the bermudagrass greens were overseeded with Gator perennial ryegrass (Lolium perenne) for winter play.

Hopkins split the nine greens, with half of each green left as an untreated check. The remaining halves received treatments of a tank mix of flutolanil (ProStar 50WP from AgrEvo) fungicide at 3 ounces, plus Primer soil wetting agent at 6 fluid ounces per 1,000 square feet. At the time, ProStar was the only fungicide labeled for fairy ring.

The tank mix was applied in mid-September 1996 and reapplied at six-week intervals through January 1997 for four preventive applications. By February 1997, necrotic and circular turf injury attributed to lectophilic fairy ring (identified as a Lycoperdon species) began to appear on the untreated half of each green.

By March 1997, no necrotic rings were observed on the halves treated with the fungicide and wetting agent, but 23 rings per green, on average, were present on the untreated side. The turfgrass quality in the untreated half of each green was considered unacceptable. A curative application of ProStar 50WP at 6 ounces, plus Primer at 6 fluid ounces per 1,000 square feet, cleared up the infected halves of the greens by May 1997, allowing the bermudagrass to recover and fill in the damaged areas.

Curative strategies
For lectophilic fairy ring, recent success has been observed with the use of a combination approach of a wetting agent, fungicide and irrigation. The wetting agent helps water move more easily through the hydrophobic soil, and the irrigation helps carry fungicide into the soil. In some cases in Southern California, however, heavy irrigation seemed to "push" the fungicide past the lectophilic mycelium in the thatch. Subsurface injection equipment may provide better placement of a control agent in the soil profile.

Fairy ring symptoms can also be suppressed through cultural practices such as aerification, deep watering and the use of surfactants to wet the soil profile thoroughly, and fertilization to promote healthy turf and mask the symptoms (7,8). Yet, fungi that cause fairy ring will probably remain viable in the soil even if these practices suppress the obvious symptoms.

Destructive methods can also control fairy ring (6,8), but they are costly, labor intensive, impractical for most situations on golf courses and not always successful. One method is removal of the affected turf, rotor-tilling and mixing the underlying soil in several directions, then reseeding or sodding the area.

Mixing the soil promotes a natural antagonism known to exist among fairy ring mycelia. For example, fairy rings have been known to dissipate when they intersect each other. Another remedy is application of a soil fumigant after the soil is mixed. Soil fumigation is an intense process, however, and proper precautions should be taken.

A second destructive method involves the physical removal of soil to 12 inches deep (6,8). Be sure to extend the excavation a few feet beyond the fairy ring. Next, fill the area with uncontaminated soil and reseed or sod.

Future direction
Research on fairy ring management includes evaluations of fungicides, soil wetting agents and cultural practices. Research also focuses on the biology and ecology of fungi that cause fairy ring in turf.

The goal is to develop strategies for maintaining healthy turfgrass and reducing hydrophobic soil conditions while controlling fungi that cause fairy ring.

Acknowledgments

Thanks to Bob Hickman of AgrEvo USA Co. for contributions to this article and to the turfgrass pathologists and golf course superintendents who commented on the occurrence of fairy ring in various parts of the country.

References

1. Couch, H.B. 1995. Diseases of turfgrasses. Kreiger Publishing, Malabar, Fla.
2. Fermanian, T.W., M.C. Shurtleff, R. Randell, H.T. Wilkinson and P.L. Nixon. 1997. Controlling turfgrass pests. Prentice Hall, Upper Saddle River, N.J.
3. Hickman, R., M. Elliott, M. Fidanza, M. Hopkins and D. Spak. 1998. A preventive approach to fairy ring disease management on putting greens. p. 145. In: Agronomy Abstracts. ASA, Madison, Wis.
4. Shantz, H.L., and R.L. Piemeisel. 1917. Fungus fairy rings in Eastern Colorado and their effects on vegetation. Journal of Agricultural Research 11:191-245.
5. Smiley, R.W., P.H. Dernoeden and B.B. Clarke. 1992. Compendium of turfgrass diseases. APS Press, Minneapolis, Minn.
6. Smith, J.D., N. Jackson and A.R. Woolhouse. 1989. Fungal diseases of amenity turf grasses. E&F Spon, London.
7. Vargas, J.M. 1994. Management of turfgrass diseases. CRC Press, Boca Raton, Fla.
8. Watshcke, T.L., P.H. Dernoeden and D.J. Shetlar. 1995. Management of turfgrass pests. CRC Press, Boca Raton, Fla.

Michael A. Fidanza, Ph.D., is a research scientist with AgrEvo USA Co., and is located in Raleigh, N.C. He began building his knowledge of fungi as a youth at his family's commercial mushroom farm in Pennsylvania, where Agaricus bisporus is cultivated.