What golfers see on a couple of fairways.

                       

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Figure 1. Yellow patch on a golf course putting green.

Yellow patch, also referred to as cool season brown patch, is caused by Rhizoctonia cerealis, a fungus closely related to the pathogens that cause brown patch and the Rhizoctonia large patch of zoysia grass.  Symptoms on putting greens can be striking (Figure 1).  They generally include small- to medium-sized patches or rings (6 to 12 inches in diameter), usually with yellow margins. Sometimes margins are reddish brown. In severe cases, patches may be distributed uniformly over putting surfaces.  In my opinion, yellow patch causes only cosmetic damage to greens height turf.  However, on surrounding turf, yellow patch infection can thin the grass, temporarily resulting in a “tight” lie that may unnerve mid-high handicap golfers.  Yellow patch occurs most often on creeping bentgrass and annual bluegrass.  Symptoms are most common on putting greens collars, and surrounds, but they may appear on fairways now and then.
Yellow patch is a cool season disease.  It is the first disease problem to appear after the snow molds. Outbreaks will most likely occur under overcast, cool, wet conditions. In the spring, symptoms often disappear after a few days of warm, sunny weather. Deliberate attempts to control yellow patch, with or without fungicides is normally not recommended because the disease has only cosmetic effects and symptoms are usually very short-lived.