Welcome to the section on brown ring patch, also known as Waitea patch, in Module 10 of our Turfgrass Disease Management course. Brown ring patch is a fungal disease caused by the pathogen Waitea circinata. It primarily affects cool-season turfgrasses during the springtime into early summer, with high humidity and temperatures ranging from 25 to 30oC (77 to 86°F). This disease typically occurs after yellow patch and before brown patch, two other common Rhizoctonia pathogens. In this section, we will explore the disease cycle, symptoms, signs, and management strategies for brown ring patch. Let’s dive in and learn more about this turfgrass disease.
Credit: PACE Turf
Causal agents
Waitea circinata fungus
Primary Hosts
This disease has been found on creeping bentgrass (Agrostis stolonifera) in Japan, but annual bluegrass (Poa annua), and roughstalk bluegrass (Poa trivialis) (to a lesser extent) are the primary hosts in the United States.
Disease Cycle
Waitea circinata survives unfavorable conditions as sclerotia or mycelium in various plant parts such as foliage, crowns, roots, and thatch. These sclerotia, which are resilient to environmental extremes, can germinate over a wide range of temperatures. The fungus is believed to spread through infected plant debris, carried by equipment, people, animals, water, or wind. When conditions become favorable, such as warm and humid weather, the sclerotia germinate and the mycelium colonizes the leaves and leaf sheaths. Mycelial growth can occur within a temperature range of 10-35°C (50-95°F), with an optimal range of 25-30°C (77-86°F). The pathogen spreads horizontally through the foliage, crown, thatch, and upper soil, forming circular to irregular patches. Under warm and humid conditions, sclerotia are formed in the crown and thatch.
Epidemiology
Brown Ring Patch symptoms typically manifest in the spring and autumn, but they may also occur during the summer if conducive conditions for infection persist. The disease thrives in warm, cloudy, and wet weather. Symptoms have been observed over a wide range of air temperatures (15-35°C or 59-95°F) on Poa annua and Poa trivialis, with most reports associated with maximum daily air temperatures of 18-29°C (64-84°F). It has been observed on Agrostis stolonifera within a similar temperature range, but can occur even at temperatures as low as 5°C (41°F).
Factors such as high humidity, poorly drained soils, and inadequate air circulation can prolong leaf wetness, thereby exacerbating disease severity. Thatch decomposition is often accelerated within the affected rings, resulting in a sunken appearance. While the pathogen primarily infects leaves, under ideal conditions for disease development, it can also affect stems, crowns, and roots, ultimately leading to plant death. Symptoms may temporarily disappear during hot summer weather and reappear in the autumn when warm and humid conditions return.
Symptoms
The symptoms of brown ring patch are most commonly observed on putting greens but can also occur on turf maintained at a higher cut, such as collars, fairways, and roughs. On fine turfgrasses like Poa annua and Poa trivialis, the disease typically manifests as thin, yellow rings or crescents in the spring. Infected leaves may retain their yellow color, which can be used in the field to differentiate brown ring patch from yellow patch, another disease caused by Rhizoctonia cerealis that occurs during cool weather. In severe cases, the affected rings can become sunken or depressed as the thatch layer degrades, which can negatively impact the playability of putting greens.
Outbreaks of the disease often appear in the spring, disappear in the summer, and then reappear in the autumn. It’s important to note that typically only one host, either Agrostis stolonifera or Poa annua, exhibits symptoms of brown ring patch at a given time. On Agrostis stolonifera, the disease appears as circular to irregularly shaped rings of tan to yellow-brown turf, with affected leaves and stems becoming water-soaked and eventually fading to tan or brown. The patches can range from 10-50 cm (4-20 inches) in diameter, and it is common for the centers of the patches to recover and turn green.
Credit: John Kaminiski/Penn State University
Signs
One of the key signs of brown ring patch is the presence of abundant white mycelium on the foliage, thatch, or upper soil layer when the turf is incubated in high humidity. The white mycelium appears as a fuzzy or cotton-like growth and is often most visible in the morning when dew or moisture is present on the turf. This mycelial growth is a characteristic sign of the disease and is produced by the pathogen, Waitea circinata. The mycelium can cover the affected areas, giving them a white or grayish appearance.
Another sign that can be observed in the field is the development of orange oblong sclerotia. These sclerotia range in size from 1 to 5 mm and initially have a white to orange color, but they may turn brown to dark brown as they age. Although sclerotia are rarely seen in the field, they readily develop within 3 to 14 days when the turf is incubated in high humidity or on suitable media.
The sexual state of W. circinata is not common, but basidiospores can be produced on the surface of V8 juice agar. The basidia, which are responsible for producing basidiospores, are 8 to 13 micrometers in length and 6 to 9 micrometers in width. They have four sterigmata, each approximately 2 to 5 micrometers long. The basidiospores themselves are 6 to 16 micrometers long and 4 to 5 micrometers wide. However, the exact role and significance of basidiospores in the disease cycle of brown ring patch are still unknown.
Credit: John Kaminiski/Penn State University
Management
The management of brown ring patch involves a combination of cultural and chemical control strategies to suppress the disease and promote turf recovery. Cultural practices play a crucial role in reducing disease severity and creating conditions that are less favorable for the pathogen’s development.
Cultural
Adequate nitrogen levels are important to reduce disease severity and encourage turfgrass recovery. Apply water-soluble, quick-release forms of nitrogen such as ammonium sulfate, calcium nitrate, and urea to suppress brown ring patch and enhance the effectiveness of fungicides. Avoid low nitrogen fertility, and fertilize the turf to avoid deficiencies of nitrogen, phosphorus, and potassium. Good management of thatch and organic matter is essential. Implement practices such as aerification, vertical mowing, and sand topdressing to control excessive thatch buildup and promote better air and water movement in the turf. Remove dew and guttation fluids from leaf surfaces by mowing, rolling, or poling greens early in the morning. This helps reduce the duration of leaf wetness, which is conducive to disease development. Promote good air circulation by pruning or removing trees, shrubs, and other barriers that restrict airflow within the turf. Improved air movement helps to reduce humidity levels and create less favorable conditions for the disease.
Chemical
Fungicides can be effective in controlling brown ring patch. Some recommended fungicides include:
- azoxystrobin
- chlorothalonil
- metconazole
- flutolanil
- fludioxonil
- polyoxin-D
- propiconazole
- tebuconazole
- triticonazole
These fungicides can be applied alone or in tank mixtures to provide effective disease control. Preventive applications are recommended in areas where brown ring patch is a chronic problem, and multiple applications may be required. Adequate spray volume and pressure should be maintained to ensure proper coverage of the plants’ bases. Adding a surfactant to enhance fungicide efficacy may be beneficial. Posttreatment irrigation can also enhance the effectiveness of some fungicides.