How to diagnose large patch

Easy to spot Large patch is characterized by irregular patches with sunken interiors that appear tan in color. (Photo: Bayer)

Large patch — formerly called brown patch — is a disease of warm-season turfgrasses, such as centipedegrass, St. Augustinegrass, seashore paspalum, zoysiagrass and Bermudagrass. One of the major fungal diseases of warm-season turf, large patch is caused by the soil-borne fungus Rhizoctonia solani and infects and rots the leaf sheaths, crowns and stolons of the turf.

According to Jim Kerns, Ph.D., associate professor and extension specialist of turfgrass pathology at North Carolina State University, large patch is relatively easy to diagnose because its symptoms are so unique. Here is what to look out for.

Symptoms: “Large patch can develop almost anywhere warm-season grasses are grown, but the disease is most severe in the transition zone or areas with prolonged humidity or precipitation,” Kerns says.

The disease creates irregular patches ranging from 10 inches to 3 feet in diameter, or larger in some cases. The perimeter of the patch displays a yellow or orange color, the patch interior becomes sunken and injured turf appears thin and tan. The plant will develop lesions on the leaf sheath, which can look different depending on the grass species that is affected. Sometimes the lesions are just necrotic — dead cells caused by severe injury or disease — like on zoysiagrass and centipedegrass, but on St. Augustinegrass, the lesions are purple in color.

If you determine turf has developed large patch, there are steps you can take to help rid it of the disease.

Treatment: Preventive fungicide applications are best for large patch, Kerns says. Time the first fall application when the average thatch temperature is 70 degrees F, or when the average soil temperature at a 2-inch depth is 72-75 degrees F.

“In North Carolina, we typically target about 75-degree F soil temperatures to initiate preventive fungicide applications,” Kerns says. “However, for those managing St. Augustinegrass or centipedegrass, preventive applications may need to target 80-degree F soil temperatures.”

A second fall application two to four weeks later is recommended to extend protection through cool, wet weather. According to Kerns, a colleague in Missouri also has found early spring application to be critical in the Midwest.

Cultural practices, such as improved drainage and regular aeration during the summer, are also important to the success of reducing large patch.