In this module, we will explore the characteristics and management strategies for yellow patch, a turfgrass disease caused by the fungus Rhizoctonia cerealis. Yellow Patch, also known as cool temperature brown patch, primarily affects putting greens but can also be found on fairways and tees. As we delve into this module, we will learn about the host plants, the specific conditions that favor yellow patch development, and the distinctive symptoms it presents, such as yellow patches with purple margins. We will examine the signs of Rhizoctonia cerealis under the microscope and discuss the cultural and chemical control measures available to effectively manage this disease.
Causal agent
Rhizoctonia cerealis
Primary Hosts
Yellow patch primarily affects certain turfgrass hosts, including annual bluegrass, creeping bentgrass, and perennial ryegrass. While it is more commonly observed on putting greens, this disease can also occur on fairways and tees.
Disease Cycle
Rhizoctonia cerealis survives in infected grass and debris. In cool or cold spring weather, typically ranging from 10-18oC (50-65oF), the disease becomes active. The fungus spreads through the production of spores and mycelium, which can infect susceptible turfgrass hosts. The infected turfgrass exhibits symptoms such as yellow patches, similar to brown patch, with purple margins. These patches can vary in size, ranging from a foot to several feet in diameter. Unlike some other diseases, the patches do not become sunken or depressed. Under the microscope, the cells of Rhizoctonia cerealis display binucleate characteristics, with typical Rhizoctonia mycelium showing right-angle branching and senescent hyphae. It is important to note that no fluffy mycelium is observed in the field or after incubation.
Epidemiology
Yellow patch prevails in cold or cool spring weather, typically occurring between 10-18oC (50-65oF). It can also manifest in the fall. The disease is more commonly observed on putting greens but may also affect fairways and tees. Yellow patch is influenced by the prevailing environmental conditions during the susceptible periods. Factors such as temperature and moisture play a crucial role in disease development. Cold or cool spring weather provides favorable conditions for the pathogen, Rhizoctonia cerealis, to infect the turfgrass and cause disease. High humidity and extended periods of leaf wetness further contribute to disease progression.
Symptoms
Yellow patch is characterized by the development of patches that are similar to brown patch. The affected areas exhibit a yellowish discoloration, hence the name “yellow patch.” The patches may vary in size, ranging from a foot to several feet in diameter. In some cases, symptoms can have the appearance of purple margins around the patches. These symptoms typically manifest during cold or cool spring weather, and in some cases, they may also occur in the fall.
Credit: John Kaminski/Penn State University
Signs
Under the microscope, the signs of the yellow patch pathogen, Rhizoctonia cerealis, can be observed. The cells of the pathogen are binucleate, a characteristic feature of Rhizoctonia species. The mycelium of Rhizoctonia cerealis displays typical characteristics, including right-angle branching and septate hyphae. However, in the field or post-incubation, there is no fluffy mycelium associated with yellow patch. The presence of these signs, along with the observed symptoms, aids in the accurate identification of yellow patch and distinguishes it from other turfgrass diseases.
Management
Yellow patch in turfgrass does not have specific cultural control practices available, necessitating the use of chemical control methods. Fungicides are the primary means of managing yellow patch and suppressing its symptoms in affected areas.
Cultural
Enhancing both surface and subsurface drainage can help reduce the severity of yellow patch. Proper drainage systems facilitate the removal of excess water from the turf, preventing prolonged periods of wetness that favor disease development. Addressing any issues with drainage, such as improving soil profiles or installing drainage systems, can be beneficial in managing yellow patch.
Removing trees or other obstructions that hinder sunlight penetration and air movement can create a more favorable environment for turfgrass growth and reduce the risk of yellow patch. Adequate sunlight exposure and improved air circulation promote faster drying of the turf, reducing the conditions conducive to disease development.
Research has shown that repeated applications of ammonium sulfate, a form of nitrogen fertilizer, can help reduce the severity of yellow patch. Ammonium sulfate not only provides essential nutrients for turfgrass growth but also exhibits suppressive effects on the disease. Proper timing and rates of ammonium sulfate applications should be followed to achieve desired results.
Credit: John Kaminski/Penn State University
Chemical
Chemical control options for yellow patch in turfgrass involve the use of fungicides to manage the disease. Fungicides such as chlorothalonil + iprodione, flutalonil, fludioxonil, and DMI fungicides are commonly employed for yellow patch control. However, it is important to note that while fungicides can be effective in suppressing the disease, symptoms may persist until environmental conditions become favorable for turfgrass growth.