A mixed bentgrass/Poa annua sample from a golf course in New England was recently submitted to the UMass Extension Diagnostic Lab. Both species showed yellowing of lower leaves. Crowns were not affected. The root system looked healthy, and no crown rot was observed. Photos of the putting green were also submitted showing pale yellow arcs and rings, some with a rust-colored edge.
The turf plug was incubated for several days on the lab bench. In that time, affected turf began to recover from the damage. Mycelium grew out of affected leaves, and eventually small buff-colored sclerotia appeared. These signs, in combination with the symptoms observed, photos of the greens, absence of other pathogens, and case history information led to the diagnosis of Yellow Patch.
Yellow Patch is caused by Rhizoctonia cerealis and is also called cool season brown patch. This disease occurs on greens from autumn through spring and is usually superficial- crowns and roots are killed only in severe cases. Symptoms appear as yellow rings or arcs, or patches. Cloudy, wet weather and temperatures 50-65°F are optimum for disease development, but the pathogen can be active at 40-70°F. Dense, highly fertilized, and over-watered turf is more susceptible.
Management: Improve soil drainage and reduce excessive thatch. Avoid excessive nitrogen applications and supply adequate levels of phosphorous and potassium for maximum plant vigor. For sites with a history of yellow patch, a nitrogen application (<0.25 lb/ 1000 ft2) in mid-late fall helps prevent early spring damage. A light application of nitrogen in spring will help affected turf recover. Minimize leaf wetness by good drainage, manual removal of dew, or pruning of trees, shrubs, and other barriers to air movement. Fungicide applications may not be necessary, as the fungus becomes inactive when temperatures reach the low 70s and the symptoms disappear; however, several products are available for management of recurrent disease. Fungicides registered for Rhizoctonia include strobilurins, demethylation inhibitors, fludioxonil, polyoxin D, chlorothalonil, and flutolanil. See the Disease Management with Fungicides section (http://ag.umass.edu/turf/professional-turf-ipm-guide/disease-management/disease-management-with-fungicides) of UMass Extension's Professional Guide for IPM in Turf for a full list of products.
Submitted by: Dr. Angela Madeiras
