Brown patch appears as circular patches, ranging from a few inches to several feet in diameter. The infected leaves first appear water soaked and dark, eventually drying, withering, and turning dark brown. A dark smoke ring often surrounds the outer margins of the diseased area when humidity is high and disease is actively growing. Leaves in the blighted area are usually killed, and the disease can rapidly kill large areas of turfgrass in short periods of time under conducive conditions.
Brown patch survives as a saprophyte in the thatch, but when soil temperatures rise above 60° F (15-20° C), the fungus will begin to grow. While growing in a circular pattern, the fungus will begin to infect turfgrass foliage when air temperatures are above 80° F (28-30° C) and when nighttime temperatures are in the 70's (21-26° C) with high humidity.