This case study comes from the research files of course author, Dr. John Kaminski:
Back in 1998, as an undergraduate at Penn State, I found myself working on a peculiar fungus that was causing significant problems in mulch beds. Known as the artillery fungus, it was my task to remove bark from various tree species to determine if certain types of mulch were more susceptible to spreading the fungus.
Fast forward to 2010, I took a golfing trip to Scotland. There, I encountered a disease they referred to as “thatch collapse.” The causal agent was unknown, and it intrigued me. Upon my return to Penn State in the fall, to my surprise, the same disease had shown up on our research greens. We often joked that the disease must have hitched a ride back on my shoes from Scotland.
Around the same time, I learned that the disease was being reported in New Zealand. Interestingly, they had contacted Don Davis, the original professor at Penn State who discovered the artillery fungus in mulch, and who I had the privilege of working for as an undergraduate.
Seeing the potential connection, Davis and I decided to collaborate to investigate this mysterious thatch collapse. We used molecular and morphological characteristics to identify the fungus and performed Koch’s postulates to confirm that this was indeed the causal agent of thatch collapse.
While this fungus isn’t an infectious pathogen, it does cause severe symptoms that can significantly impact the playability of golf course putting greens. The discovery was a significant breakthrough, linking my past and present work in a fascinating twist of scientific fate. It was a reminder of how interconnected our world is and how a curious mind can lead to unexpected discoveries.
Credit: John Kaminski/Penn State University
Causal agents
The causal agent of thatch collapse is Sphaerobolus stellatus, a wood-rot fungus commonly found in home landscapes. It produces creamy white mycelia and, if present, white to creamy orange basidiocarps (fungal fruiting bodies) measuring 1-3 mm in diameter. The basidiocarps contain spore masses (glebae) that can be forcefully ejected up to 6 m. The basidiospores of S. stellatus are approximately 7.6 x 4.8 um in size.
Primary Hosts
Thatch collapse is a disease of all fine turf mowed to a height of 1.3 cm or lower. It affects most turfgrass species and has been identified throughout the United States, The United Kingdom, Australia, and New Zealand.
Disease Cycle
Sphaerobolus stellatus survives unfavorable conditions as hardened glebae and/or mycelia within the soil profile. Glebae are highly tolerant of environmental extremes and can survive for several years. When conditions are favorable, the fungus spreads radially through the thatch. Although it does not directly infect turfgrass plants, it aggressively degrades organic matter as it moves laterally. This results in the sunken, dark green areas characteristic of thatch collapse. Under optimal conditions, up to 20% of the surface organic matter can be lost in as little as 6 weeks.
Epidemiology
Thatch collapse is most severe in areas where thatch accumulation is excessive. The optimal temperature range for the growth of S. stellatus is 21 to 30°C (70 to 86°F), but it can grow at temperatures as low as 5°C (41°F). Symptoms may appear throughout the year but are generally more severe from late spring to early fall. The disease is favored by extended dry periods followed by heavy rains or periodic wet-dry cycles. The forceful discharge of glebae several meters from an individual infection center likely plays a significant role in the spread of the disease.
Symptoms
Thatch collapse in both cool- and warm-season grasses manifests as depressed or sunken patches of dark green turf, typically measuring 8 to 46 cm or more in diameter. Active patches may exhibit a yellow or lime-green ring at the outer edge.
Credit: John Kaminski/Penn State University
Signs
Cross-section examination of the affected area reveals a fawn-colored mycelium in the top 2.5 cm (1 in) of the thatch. Occasionally, basidiocarps, which are fungal fruiting bodies, may form near the crowns of affected turfgrasses.
Credit: John Kaminski/Penn State University
Management
Little is known about the management of this relatively new disease. Cultural and chemical practices typically implemented to control fairy ring are generally recommended for suppression of thatch collapse.
Cultural
Thatch collapse, much like fairy ring, is a turfgrass disease that can be effectively managed through a series of cultural practices. These practices are designed to not only maintain the overall health of the turf but also reduce the conditions that are conducive to the development of the disease and manage the symptoms when they do occur.
One of the key cultural control strategies for thatch collapse is the regular application of a balanced fertilizer, particularly one that is high in nitrogen. Nitrogen promotes vigorous growth and enables the turf to recover quickly from the damage caused by the disease. However, it’s crucial to strike a balance and avoid over-fertilization as this can lead to an excessive accumulation of thatch, which in turn can exacerbate the problem of thatch collapse.
Another important cultural control measure is topdressing. This involves the application of a thin layer of soil or sand over the turf. The practice of topdressing can help to smooth out the surface depressions that are caused by thatch collapse, thereby improving the overall appearance and playability of the turf. Topdressing also aids in the breakdown of the thatch layer by bringing microorganisms from the soil into direct contact with the thatch.
In addition to these measures, regular aeration can help to manage thatch levels and improve the overall health of the turf. Aeration helps to break up compacted soil and thatch, improving water, nutrient, and oxygen movement into the soil. This can stimulate the growth of beneficial microorganisms that help to decompose thatch.
Chemical
Little is known about fungicidal control of thatch collapse. Fungicide recommendations generally include those specified for the suppression of fairy ring.