Richard Latin, Turf Pathologist, Department of Botany & Plant Pathology, Purdue University
Brown patch is a fungal disease of turf that occurs during hot humid weather. Moderate to severe outbreaks on high-maintenance creeping bentgrass and annual bluegrass can result in thin, poor quality turf that may be predisposed to algae and moss infestation. Brief episodes of brown patch activity can temporarily spoil the appearance of putting greens, tees and fairways. Taller mown turfgrasses for athletic fields and professional landscapes, especially tall fescue and perennial ryegrass, also may sustain damage from brown patch infection.
On creeping bentgrass and annual bluegrass putting greens and tees, brown patch development results in well-defined circular patches, ranging from 4 to 12 inches in diameter. Leaf blades within the patches turn brown after infection, while a gray-white band may be evident at the perimeter of active patches. Images of brown patch field patterns and symptoms are described in my Turf Disease Profile on brown patch (BP 106-W) available at the Turf Pathology webpage.
Click on image to enlarge
Yellowish/brown cast and thinning caused by Rhizoctonia
Close-up of Brown Patch symptoms
Individual leaf lesions caused by Rhizoctonia