Turfgrass Diseases: Cool-Season Brown Patch or Yellow Patch (Causal Fungus: Rhizoctonia cerealis)

This disease is caused by the fungus Rhizoctonia cerealis and is often found on golf course putting greens and tees during years where snow cover lasts for long periods during mid to late winter.

Symptoms

Cool-season brown patch symptoms are typically noticed after snow cover melts and exposes turfgrass in late winter or early spring. Symptoms include light-brown, reddish-brown, or yellow rings surrounding patches of blighted or partially blighted turf. Patches may be circular or irregularly shaped, ranging from a few inches to 3 feet in diameter, sometimes coalescing to affect large areas of turf.

Disease Cycle

Rhizoctonia cerealis survives adverse environmental conditions as thick-walled mycelial cells called bulbils. Bulbils remain dormant in decaying plant litter, thatch, and soil during warm periods, then give rise to actively growing mycelium in cool, wet weather during late fall, winter, or early spring. Mycelium spreads through thatch resulting in infections of grass leaves, sheaths, and stems. In severe cases, the pathogen can infect crown tissues and kill plants. The disease most often occurs under snow cover but does not require snow cover for symptom development.

Disease Development

Cool-season brown patch is commonly found on golf course putting greens and tees during winters with prolonged snow cover. Ideal conditions for the development of this disease include low temperatures, wet conditions, and cloud cover. Although all cool-season turfgrass species can be affected by cool-season brown patch, annual bluegrass, creeping bentgrass, and perennial ryegrass are most susceptible.

Cultural Control

Cultural practices that may lessen the severity of this disease include using only moderate amounts of nitrogen fertilizer in fall, reducing excessive thatch accumulations, and facilitating drying of foliage by mowing and removal of greens covers on sunny days in early spring.

Chemical Control

Preventative fungicide applications can be used to control cool-season brown patch on high-value turf, such as golf course putting greens and tees. To obtain successful control when disease symptoms appear under snow cover, fungicides need to be applied prior to the first permanent snow cover in the fall, typically in late November. Applying fungicides after cool-season brown patch symptoms appear in the spring can arrest the disease and prevent further injury.

Table 1. Some penetrant fungicides labeled for control of cool-season brown patch

Table 2. Some multisite contact fungicides labeled for control of cool-season brown patch

Table 3. Some combination product fungicides labeled for control of cool-season brown patch

*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 the 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 a 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.

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

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

Smiley, R.W., P.H. Dernoeden, and B.B. Clarke. 2005. Compendium of turfgrass diseases, 3rd Edition. American Phytopathological Society Press, St. Paul, MN.