Brown Patch (fungus – Rhizoctonia solani)
Host Grass: Hybrid Bermuda(Cynodon dactylon), Common Bermuda, Bentgrass(Agrostis palustris), Centipede Grass, Fescue, Perennial Ryegrass(Lolium perenne), Poa Series(Poa sp.), St. Augustine Grass(Stenatophrum secundatum), Zoysiagrass(Zoysia japonica)
Cause and Symptoms: The name, brown patch, is not very descriptive of the varied symptom expression caused by Rhizoctonia spp. on turfgrass. Symptoms differ on cool- and warm-season grasses and vary depending on environmental conditions and cultural practices. Turfgrass affected by brown patch generally will exhibit circular or irregular patches of light brown, thinned grass. On cool-season grasses (bent, rye and fescue) during periods of warm, humid weather, a darkened border or smoke ring may develop at the outer margin of the patches. The smoke-ring symptom is not reliable for diagnosis. Symptoms on warm-season grasses such as bermuda grass or St. Augustine grass include circular to irregular patches of blighted turf. Patches up to several yards in diameter commonly develop in the fall, winter and spring when these grasses are approaching or emerging from dormancy, evening temperatures are below 68oF, and rainfall usually increases. Active infections are noticeable by yellow leaves at the edges of patches. Leaf sheaths become rotted, and a gentle tug on the leaf blade easily separates the leaf from the runner. Brown patch usually does not discolor roots. Disease develops most rapidly when air temperatures are between 75oF and 85oF and wet conditions are present and generally subsides when air temperatures rise above 90oF.
Control and Management: Water only as needed and early in the day to remove dew and allow the grass to dry quickly. Avoid over fertilization in spring and fall. Improve the turfgrass root system with good drainage and aeration to reduce damage caused by brown patch. Fungicides (See the section Chemical Controls for Turfgrass Diseases) are most effective when used on a preventive basis.
Content edited by: Young-ki Jo, firstname.lastname@example.org , Assistant Professor and Extension Specialist, Dept Plant Pathology & Microbiology, Texas A&M University, Texas AgriLife Extension Service, May 31, 2013