One of my favorite names for a common turfgrass malady is fairy ring. In medieval folklore, it was believed that fairies dancing at night in a circle left these symptomatic rings of damaged or stimulated grass with or without mushrooms the next morning.
There are many different species of fungi that can cause these visual symptoms, which is probably why sometimes fungicides work and sometimes they don’t. The most difficult aspect of managing fairy ring is when the fungal mycelium “clogs” the pore space of the soil and prevents water from entering. This impedes delivery of products via water to remedy the problem. The fungus is essentially sucking-up all the water and also creating hydrophobic conditions in the rootzone that lead to desiccated, dry turf as one of the most damaging symptoms of fairy ring.
This summer, I have gotten more calls than normal about fairy ring outbreaks directly following aeration, especially after vertical mowing. Root assays reveal their efficiency and health are negatively impacted following aeration compared to earlier or later in the year. This is not to say that aeration should be discontinued, but it does indicate that aeration can impact turfgrass as a significant stress. Aeration also likely generates an opportunity for any fungi in the soil to colonize cut or wounded and damaged stolons, rhizomes and roots. I remember when farmers in my hometown baled hay from their wheat fields, they would leave the hay to dry in the sun before bringing it into the barn for fear that it would rot if stored wet. I think a similar situation may apply to the fresh, damaged organic matter that results from aeration and vertical mowing of turfgrass putting greens. Following aeration with a watered-in fungicide application may be a good idea, especially if fairy ring has been a problem.
Even if the fungus causing fairy ring symptoms is killed by a fungicide application, the dead fungal mycelium is essentially hydrophobic thus contributing to soil water repellency in the rootzone which results in necrotic turf injury. This can leave one wondering whether the fungicide treatment actually was effective or not. An easy way to determine if additional applications are warranted is to take small-diameter plugs from within and just outside of the symptomatic ring zones. Wrap them in a wet paper towel and place them in either a sealable plastic bag or plastic container at room temperature for 48 hours. While fungal growth doesn’t necessarily mean it’s the fungus that caused the fairy ring, the visual proliferation of any mycelium indicates that if a broad-spectrum fungicide was applied, it probably didn’t actually get to the fungus.
For successful curative control of fairy ring, it is absolutely essential that the wetting agent and/or fungicide is delivered to where the fungus is located in the soil, more so than what product is used. This is the challenge. Needle-tine aeration followed by wetting agent applications that are hand watered in – alone or with a fungicide – have a better chance of getting into the mycelium-coated pore space than applications watered-in with overhead irrigation. If water is sheeting off the afflicted area, your efforts and costs associated with treatments are being wasted.
The best method of controlling fairy ring is never letting it get established. Monitoring and maintaining consistent moisture levels with the use of wetting agents helps foster a strong root system, as well minimizing the impact of wet or dry weather patterns. A strong root system will facilitate more soil moisture consistency and leave little chance for an opportunist that is better suited to children’s books and mythology than putting greens.
Southeast Region Agronomists:
Chris Hartwiger, director, USGA Course Consulting Service – chartwiger@usga.org
Steve Kammerer, Ph.D., senior consulting agronomist – skammerer@usga.org
Jordan Booth, agronomist – jbooth@usga.org