Turfgrass Diseases: Brown Ring Patch (Causal Fungus: Waitea circinata var. circinata)

Brown ring patch is caused by the fungus Waitea circinata var. circinata, a species closely related to the causal pathogens of brown patch and yellow patch diseases. This disease produces yellow circular patches, similar in appearance to summer patch and necrotic ring spot. Brown ring patch has been in the United States since at least 2007, and perhaps as early as 2003, and only limited information is available on cultural and chemical control measures.

Symptoms and Signs

Brown ring patch is most problematic on close-cut annual bluegrass and less common creeping bentgrass. Symptoms appear as yellow rings or patches that range from a few inches up to 3 feet in diameter. The causal fungus of brown ring patch, W. circinata var. circinata, attacks the leaves, stems, and crowns of turfgrass plants. It does not produce spores on diseased plants but does form mycelia with right-angle branching, which are only visible with the aid of a microscope.

Disease Cycle

Limited information is available concerning the disease cycle of brown ring patch. Presumably, W. circinata overwinters as sclerotia in infected grass tissue or in soil. As conditions become conducive for disease development, mycelia infect leaf, stem, and crown tissues and initiate disease activities. Mycelia spread from plant to plant, infecting new tissues and forming patches of diseased annual bluegrass when humidity is high in late spring and early summer.

Disease Development

In Pennsylvania, brown ring patch occurs on annual bluegrass putting greens in May or June under a wide range of temperatures (60 to 95°F) and during overcast and humid conditions. This disease is not typically observed during mid-summer or fall.

Cultural Control

Very little research-based information is available concerning cultural control measures, although some reports indicate brown ring patch may be more severe under low nitrogen fertility. Applying small amounts of nitrogen with fungicides has been shown to improve fungicide efficacy. At least one research report indicates a slight increase in brown ring patch symptom development following applications of trinexapac ethyl growth regulator. However, when trinexapac ethyl products are combined with nitrogen before disease activity begins, less disease and improved putting green quality have been observed. Irrigating turf at night during humid conditions may exacerbate brown ring patch; thus, watering should be done in the early morning or at other times of the day in time for the grass to dry before nightfall. In cases of persistent brown ring patch, efforts should be made to promote creeping bentgrass over annual bluegrass in putting greens.

Chemical Control

Relatively few fungicide trials have been conducted for brown ring patch control. Hence, our understanding of which products provide the best suppression and optimum timing of applications is limited.

*FRAC is an abbreviation for Fungicide Resistance Action Committee. The FRAC code/resistance group system consists of numbers indicating classes or groups of fungicides based on mode of action, and letters that refer to broad classifications of fungicides (P = host plant defense inducers; M = multi-site fungicides; and U = unknown mode of action and unknown resistance risk). Due to the risk of fungicide resistance, turf managers should avoid excessive use of fungicides within the same FRAC code/resistance group and alternate products among different FRAC codes/resistance groups.

**Plant mobility classification refers to a fungicide’s ability to penetrate plant surfaces or remain on plant leaf or stem surfaces without penetration. Fungicides that penetrate plant surfaces and are translocated mostly upwards through plant xylem tissues are called acropetal penetrants (acropetal = toward the apex). Fungicides that enter plant cuticles or move limited distances in internal plant spaces, but do not translocate through vascular tissues (xylem and/or phloem) are called local penetrants. Contact fungicides do not penetrate plant surfaces and only inhibit fungal pathogens residing on leaf and stem surfaces.

***Follow label precautionary statements, restrictions, and directions regarding tolerant turfgrass species, rates, and timing of applications.

References

Buhler, W. Fungicide spraying by the numbers.

Chen, C.-M., G.W. Douhan and F.P. Wong. 2007. First report of Waitea circinata var. circinata causing brown ring patch on Poa trivialis in California. Plant Disease 91:1687.

Clarke, B.B., P. Koch, and G. Munshaw. Chemical control of turfgrass diseases 2024. The University of Kentucky, Rutgers University, and The University of Wisconsin.

Latin, R. 2011. A practical guide to turfgrass fungicides. American Phytopathological Society Press, St. Paul, MN.

McDonald, S., D. Settle, L. Stowell, C. Chen, and F. Wong. 2009. Chemical control of brown ring patch. Golf Course Management. 82–88.