Pathogen: Rhizoctonia sp.
Host: This disease affects most major turfgrasses and is very prevalent in the South, where extended periods of high temperatures and high humidity frequently occur. Under favorable conditions, this disease can quickly destroy both aesthetic and service qualities of a turfgrass stand. All turfgrasses are susceptible and there are no resistant varieties.
Symptoms: (see photos 1 & 2 below) Symptoms vary with combinations of turfgrass variety, soil conditions, humidity and fungal strain. Home lawns and golf course fairways that are cut at normal heights have brown, circular patches ranging from 1 to 9 feet in diameter. Under drier conditions, the affected areas may be smaller and appear sunken because diseased leaves have collapsed. Grass in the center of such patches may be unaffected or may recover more rapidly than grass at the margins. This results in ring or doughnut-shaped areas. Sometimes a circular patch is not evident. In such cases, a large area may be thinned and eventually killed by the pathogen. On cool-season grasses, leaf lesions of various sizes and shapes with diffuse, dark brown borders develop. The lesions are most frequently seen on grass blades at the margin of the patch. Cool season grasses are most frequently affected during the heat of summer.
1. Brown Patch on Fescue 2. Foliar Symptoms on Fescue
Pathogen cycle: The fungus overwinters as small, hard, brown to black resting bodies (sclerotia) that are resistant to cold, heat, drought and chemicals. They can survive many years in soil. Growth of the fungus from sclerotia onto moist leaves and sheaths occurs when daily air temperatures approach 73 F. When air temperatures reach 80 to 85 F, the humidity is high and free moisture is present, disease spread is rapid.
Management: Disease severity is greater on turfgrasses grown at high nitrogen levels, than those grown with normal, balanced fertility, so a balanced fertility program is important in disease prevention. Water management is another important cultural control. It’s best to water when drying conditions are favorable and to irrigate thoroughly, but only as frequently as is needed to maintain a healthy turf. Provide good surface and subsurface drainage.The active ingredients flutolanil, triadimefon, PCNB, propiconazole, fenarimol, mancozeb, myclobutanil, and thiram are listed for use in the HGIC publication on brown patch management. Look for products that contain these fungicides as an active ingredient. See http://hgic.clemson.edu/factsheets/hgic2150.htm for the complete document. Commercial growers can also refer to the 2006 Pest Control Guidelines for Professional Turfgrass managers. It is available online at www.clemson.edu/turfornamental/.