IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Fairy Ring

Pathogen: Numerous fungi in the Basidiomycetes
Hosts: All turfgrass sites

Symptoms and signs

Fairy rings are usually first noticed as irregular rings or arcs of darker green grass on the turf surface (Figure 1). The darker color is caused by the release of nitrogen as the fairy ring fungus breaks down organic matter. The margins of the rings are often irregular or wavy. On putting surfaces especially, the entire area defined by the ring may be darker green than the surrounding uncolonized area (Figure 2).

The rings can remain green or progress to the point where dead grass develops at the margin (Figure 3). Death of grass at the margin has been attributed to moisture stress due to hydrophobic soil conditions that develop as the fairy ring fungus grows. The death has also been linked to excess nitrogen release or the formation of hydrogen cyanide or other toxic metabolites. With some fairy rings, death of the grass also occurs in spots where the fruiting bodies have emerged and then collapsed (Figure 4). Fairy ring with resulting loss of turf is one of the most destructive diseases occurring on putting surfaces.
Where two or more rings meet, the margins of the individual rings are incomplete (Figure 4). Rings are also disrupted by changes in soil type (Figure 5) or by impediments such as cart paths or sidewalks. When rings form on a hillside, the bottoms of the rings are not closed.
Fruiting bodies associated with the causal fungus may or may not emerge. Fruiting bodies found on putting surfaces are often puffballs that form at the outer margins of the rings (Figure 6). Other fairy ring fungi, especially those in pastures or other areas of higher cut turf, produce larger and more spectacular mushrooms (Figure 7).

Conditions

Fairy rings are elusive, often visible one year and not the next. Under some environments, fairy rings are visible every year. The factors that favor symptom expression and the growth and development of the fairy ring fungi are not well understood. Until recently, identification of the fungal species causing fairy ring in a given environment has keyed on fruiting body morphology and spore color, size and shape. Recent advances in genetic techniques have allowed for identification of some species without the presence of fruiting bodies, but this is not a widely available diagnostic tool.
Although the biology of the fairy ring fungi is not well understood, certain generalizations can be made. Fairy ring symptoms are usually more noticeable in nitrogen-deficient turf, simply because more nitrogen is available to the turfgrass plant in areas where the fairy ring fungus is decomposing organic matter.
Fairy ring is more commonly observed under heavy thatch. Fairy ring has been observed on all soil types, but is more common on sand-based putting surfaces. Fairy ring is especially abundant following new construction or renovation, presumably because of low population levels or lower diversity of competitive or antagonistic microorganisms. Nevertheless, fairy ring can also occur on older putting surfaces, especially under heavy thatch or where severe layering is an issue. Greens topdressed with fine sand are also more prone to fairy ring.
Moisture is important to fairy ring development and symptom expression. Type 2 rings are more likely to progress to damaging Type 1 rings when moisture is limiting. Ring margins typically fire on windy days with low relative humidity. Once browning has occurred, the soil is difficult to rehydrate. Fruiting bodies are more common under wet, humid conditions.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.