Spring Turf Patches
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Rhizoctonia Spring Patches
Brown Ring Patch
Brown ring patch is a disease of annual bluegrass on putting greens. Damage is largely cosmetic, although in some areas smoothness and uniformity of putting surfaces are disturbed, warranting chemical control. The duration of symptom expression usually is brief (one or two weeks), and coincides with mild weather with ample moisture. Despite its common name, the disease first appears as clusters of yellow rings that selectively attack annual bluegrass. Leaves of affected plants may begin to die after several days, so the yellow rings may change to a reddish brown color. Brown ring patch may be confused with yellow patch, a disease caused by a related fungal pathogen that occurs under cooler temperature regimes and infects creeping bentgrass as well as annual bluegrass. Identification of brown ring patch is primarily based on the yellow ring field pattern affecting only annual bluegrass during mild and wet springtime weather. No distinguishing lesions are evident on leaves, and mycelium is visible only under laboratory grade magnification. The brown ring patch pathogen was identified as Waitea circinata var. circinata in 2005. In some cases it is referred to as "Waitea patch".
Brown ring patch is more likely to occur on turf approaching nitrogen deficiency. Therefore, maintaining adequate nitrogen in mid- late spring may reduce severity and duration of symptom expression and may hasten turf recovery upon the arrival of dry sunny weather. Fungicides normally effective against Rhizoctonia diseases such as brown patch and Rhizoctonia large patch have performed well against brown ring patch in several research trials. However, only one fungicide (polyoxin d) is currently registered for use against the disease.
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. Although symptoms can be striking, yellow patch causes only cosmetic damage and does not affect playability. It 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 symptoms are readily identified by small to medium-sized patches (6 to 12 inches in diameter), usually with yellow margins. Sometimes margins are reddish brown. In severe cases, patches may be distributed uniformly over the putting surface. Unlike brown ring patch, which does not affect creeping bentgrass, yellow patch seems to infect bentgrass and annual bluegrass equally.
Yellow patch is a cool season disease, so there have been numerous reports in the Midwest during the past 2 months. Symptoms most often appear in early to mid-spring, but sometimes occur in mid-fall. Outbreaks will most likely occur under overcast, cool, wet conditions. In the spring, symptoms will readily disappear after a few days of warm, dry 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. There are several effective products (Prostar, QoI fungicides, and DMI fungicides) for those cases where the fungicide option is warranted.
Rick Latin, Turfgrass Pathologist