Fairy ring is a widespread and complex turfgrass disease affecting both cool-season and warm-season grass species worldwide. It is caused by various basidiomycete fungi that inhabit the thatch and soil. Unlike other diseases, fairy ring fungi do not directly harm turfgrass plants but instead alter the physical and chemical properties of the root zone, leading to changes in turf health and appearance. Managing fairy ring requires controlling the causal fungi and remedying soil conditions to restore turfgrass health.
Fairy ring occurs in different “types” depending on the symptoms it produces. Type 1 fairy ring produces circular arcs or rings of wilted or dead grass. Type 2 fairy ring produces dark green rings of stimulated turfgrass growth. Type 3 fairy ring produces rings of mushrooms.
Credit: SciShow
Causal agents
Fairy ring is caused by various basidiomycetes in the order Agaricales. These fungi include species of Agaricus, Agrocybe, Arachnion, Bovista, Calvatia, Chlorophyllum, Clitocybe, Coprinus, Hygrocybe, Lepiota, Lycoperdon, Marasmius, Panaeolus, Scleroderma, Tricholoma, and Vascellum.
Primary Hosts
Very widespread, warm and cool season species world-wide are affected. Fungi do not infect or cause direct harm to turfgrass plants. Instead, fairy ring fungi colonize the thatch and soil and alter the physical and/or chemical properties of the turfgrass root zone, which in turn elicits a change in the health or appearance of the turf.
Disease Cycle
The initiation of fairy ring is not fully understood, whether it begins with fungal mycelium or the germination of basidiospores. Once established, the fungus grows radially outward, colonizing the thatch and upper root zone. Fairy ring fungi can penetrate deep into the soil, with a dense network of mycelia reaching depths of 20 cm or more. Symptoms occur in three zones:
- outer stimulated zone: where organic matter decomposition releases nitrogen
- inner stimulated zone: where nitrogen release from older mycelium stimulates turf growth
- dead zone: caused by hydrophobic conditions, drought stress, or toxic compounds in the root zone
Epidemiology
Fairy ring is more prevalent and damaging in areas with low fertility and insufficient soil moisture. It tends to occur more severely on turf that is lightly watered and underfertilized, such as golf turf, sports fields, and lawns. Turf with thick thatch layers and those grown in sandy soil are particularly susceptible to fairy ring development. However, regions with high rainfall may have fewer rings compared to drier areas, possibly due to the presence of microorganisms that are antagonistic to fairy ring fungi. Consistent and uniform soil water content can help suppress fairy ring, while environmental conditions that cause wet-dry cycles are associated with persistent occurrence of the disease.
Symptoms
Fairy ring is characterized by the presence of rings, semicircles, or arcs of darker green or faster-growing grass (Type 2) in the affected areas. These symptoms can be observed throughout the year, but are more prominent when soil moisture is plentiful. The outer zone of the fairy ring may exhibit dead or damaged turf (Type 1), while the inner zone may show thin or dead grass or another zone of stimulated growth. In some cases, mushrooms or puffballs may emerge in the outer zone (Type 3).
Credit: John Kaminski/Penn State University
Signs
Signs of fairy ring include the appearance of rings, semicircles, or arcs of darker green or faster-growing grass. In some cases, mushrooms or puffballs may emerge in the outer zone of lush grass. Infested thatch and soil may have a distinct mushroom odor, and the soil beneath the affected turf can become extremely dry due to water repellency.
Credit: John Kaminski/Penn State University
Management
Fairy ring is a challenging turfgrass disease that manifests as a visible ring or arc pattern in the turf. Effectively managing fairy ring requires a combination of cultural practices and chemical treatments. Cultural strategies focus on implementing sound agronomic practices to create an environment less favorable for fungal growth and to improve soil conditions. By integrating cultural and chemical management strategies, turfgrass professionals can effectively suppress fairy ring and maintain healthy and aesthetically pleasing turfgrass.
Cultural
One key approach is to fertilize the affected turf with nitrogen or iron. Proper fertilization can help mask the symptoms of the disease and promote healthier turf growth. Alongside fertilization, appropriate irrigation practices are crucial in managing fairy ring. Providing a consistent and steady moisture supply in the root zone of the turf can help prevent extreme fluctuations between overly wet and dry conditions. This consistency aids in reducing the severity of the disease and its effects on the turf.
Other important cultural methods for fairy ring control are aerification and topdressing. By regularly performing aerification, turfgrass managers can reduce thatch depth and improve water infiltration into the soil. These practices contribute to creating a healthier and more resilient turf, making it less susceptible to fairy ring. Additionally, topdressing can further enhance the soil’s condition and support the turf’s recovery from the disease.
Chemical
While cultural practices play a significant role in managing fairy ring, chemical control methods can also be utilized for more targeted and specific treatment. Fungicides are commonly employed for controlling fairy ring, particularly on putting greens or other turfs that are managed at or below 0.25 inches in height. However, fungicidal control of fairy ring can be inconsistent, and turfgrass managers are advised to carefully evaluate whether it is the best course of action for their particular situation.
When applying fungicides for fairy ring control, certain considerations need to be taken into account. Research suggests that a single fungicide application may not provide effective disease control. Instead, two to four sprays are often necessary to achieve significant reductions in disease severity. Therefore, turfgrass managers should decide whether to apply multiple treatments or avoid fungicides altogether based on their specific situation.
Careful selection of fungicides is necessary for effective control of fairy ring. While some fungicides suppress the growth of fungi causing fairy ring, other cultural practices such as aerification, nitrogen fertility, and the use of wetting agents may also be required to alleviate the symptoms. Research indicates that high-volume applications of fungicides, along with the use of wetting agents, may be beneficial for preventive and curative treatments.
It is crucial to recognize that numerous fungi can cause fairy rings, and some may not be sensitive to fungicides at normal use rates, while others may be deep in the soil and unaffected by the treatment. As such, turfgrass managers should be mindful of these factors when planning a control program for this complex disease.
Fungicides that have shown to be most effective come from the following chemical classes or combinations:
- QoI
- DMI
- polyoxin
- select SDHI (flutolanil, fluxapyroxad)
In sites with chronic fairy ring outbreaks, two spring applications of a DMI fungicide on a 21-28 d interval after the first true mowing (turf begins growing) may be beneficial.