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Necrotic Ring Spot Necrotic Ring Spot (Leptosphaeria korrea) is a turf disease which affects local bluegrass lawns. In our area, this disease has been referred to as an Ophiobolus patch or take-all patch disease. In other areas of the country it has been confused with Fusarium blight. Symptoms: New outbreaks of NRS usually appear late spring to early summer and early fall as small, circular, chlorotic areas with thinning or dying of the grass. The infected turf is easily lifted from the soil and the roots and shoots of the plants eventually die, creating a dead patch. Initially, patches are several inches in diameter but can expand to form rings, arcs, or larger patches up to several feet. Actively expanding patches generally have a border of reddish-brown turf. Weeds and unaffected grasses often invade the center of the patches creating a doughnut-like effect. The disease is inactive during mid-summer and the turf can appear to recover, but the same ring spots usually reappear in the fall. NRS is most commonly seen in our area on two to five year old bluegrass turf that was established from sod, but can sometimes be seen on straight bluegrass seeded lawns. Highly fertilized, over-watered and heavy thatched lawns seem to be more subject to attack. Cultural and Nutritional: 1. The recommended fertilization rate of bluegrass-type turfs in Spokane County is 4 to 6 lbs of actual nitrogen for every 1,000 sq ft at each application. The best timing is March, April, June, September and November for applications. A good fertilizer to use is Ritters Superturf. It will provide 5 1/4 lbs of nitrogen per 1,000 sq ft each year as well as needed sulfur and other trace elements. 2. A healthier turf results when it is watered less frequently but more deeply. Turf that tends to be watered every day, whether it needs it or not, is usually over watered. Water the turf only when the top two inches of soil are dry, when the lawn indicates by turning a blue-green color or by not springing back when walked across. 3. Heavy thatch in a lawn can prevent water, fertilizer and air from reaching the roots of the grass which creates an unhealthy situation for a lawn and an environment for NRS to live and thrive. Thatch should be removed by power raking and plugging when it becomes more than 1/4 to 1/2 inch thick. 4. Keep your lawn healthy, but don't over do it. Follow good lawn care practices. Water carefully. Resistant Varieties: Perennial rye grasses and tall fescues appear to be resistant to NRS. There have been greenhouse studies that suggest certain varieties of bluegrasses are fairly resistant to NRS such as Adelphi, Park, Majestic, Able-1 and Allure-Ba. Starting a turf lawn or over seeding with those resistant varieties would be a good idea to try to minimize NRS development. |
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