NECROTIC RING SPOT

• Pathogen:  Leptosphaeria korae
• Grasses Affected:  Annual bluegrass (Poa annua), creeping bent grass (Agrostis palustris), Kentucky bluegrass (Poa pratensis), Chewing’s fescue (festuca rubra var. commutata), red fescue (Festuca rubra), perennial ryegrass (Lolium perenne).
• Season of Occurrence:  Late winter, spring and fall.
• Symptoms and Signs:  In the early stages of disease development, necrotic ring spot is seen as irregular patches of grass that have a general appearance of drought injury.  The plants are often stunted or discolored and turn various shades of red, yellow, or tan.  These areas become dull tan to brown as the disease progresses.  The shapes of the individual patches of dead grass are usually more or less circular in outline.  They may range in size from 2-3 inches (5-8 cm) to 2-6 feet (0.6-2 m) in diameter.  At first, leaf death is usually uniform throughout the affected area.  However, as the disease progresses, many of the patches may develop center tufts of apparently disease-free grass.  This combination produces a distinctive frogeye effect.  During weather conditions that are particularly favorable for outbreaks of necrotic ring spot, reddish borders may develop between the patches of dad plants and the adjacent healthy grass.   The diseased plants can be easily lifted from the soil.
• Conditions Favoring Disease Development:  Development of necrotic ring spot is generally most active during the cool, wet weather of spring and fall.  During April and May, heavy outbreaks of the disease have been noted more destructive in stands of turf grass under high nitrogen fertilization.  The severity of the disease is not affected by soil pH’s in the 5.0-8.0 range.  Outbreaks of necrotic ring spot are usually most prominent in three to four year old turfs.  Spread of the pathogen to new sites is accomplished primarily by the transport of infested soil and diseased crown and root tissue on coring, vertical mowing, and power raking equipment.
• Control: (1) Cultural Practices – Necrotic ring spot is most severe on Kentucky bluegrass, annual bluegrass, and creeping red fescue.  During the months of spring and early fall, golf greens or bowling greens with high populations of annual bluegrass should be carefully monitored for outbreaks of this disease.  management practices that promote deep rooting of the turf grass during periods of new root growth (spring and fall) will aid materially in reducing the severity of outbreaks of necrotic ring spot.  (2) Call Empire Tree and Turf for a free estimate for a fungicidal program for your turf grass.