November 13, 2018 | Lawn Care Tips

Necrotic ring spot in the lawn: let’s cope with it

Necrotic ring spot in the lawn: let’s cope with it

Necrotic ring spot also dubbed NRS for short appears to be one the most destructive grass diseases. The given disease also impacts annual bluegrass and red fescue. NRS is particularly harmful to bluegrass due to the fact that it’s a perennial issue and the fungus impacts and kills the crowns and roots.


NRS often shows up 2-3 years after lawn establishment. However, it mightn’t develop in a lawn for up to ten years or even more. In fact, symptoms of the disease might be evident throughout the growing season, although they normally escalate in late July or August. First, light green or straw-colored patches or spots a couple of inches to several feet in diameter show up on the lawn. The given patches can be localized to just one part of the lawn or widely scattered throughout your land. As NRS progresses, plants at the patch margin start dying off and get matted whereas the plants inside the ring stay green and healthy. As a result, the patches get a frog eye or doughnut pattern. Eventually, existing patches are prone to gradually developing a bright yellow ring. After this, the affected plants die off. Those patches developing in shady areas or spots with excessive thatch face greater damage and come with a crater-like appearance. Later, rings can join each other by generating larger arcs of dead grass.

Bluegrass impacted by this disease demonstrates extensive root as well as crown discoloration and also rot. It can be observed by cutting a tiny sod piece from the lawn and cautiously washing off soil as well as organic matter from the plants’ roots. With the help of a hand lens, you can spot darkly pigmented fungal threads on the root surface. However, it can be hard to view because
bluegrass roots normally feature brown coloration.

The symptoms can arise in early September, although the turfgrass can recover during late autumn and the following spring until those rings aren’t visible any no longer. However, due to its perennial nature, the disease can reappear and escalate in mid-summer later.

What causes it?

The disease is provoked by a soil-borne fungus dubbed Ophiosphaerella korrae. The given fungus is capable of surviving from year to year on colonized, dead bluegrass roots as well as crowns and also on the surface of living roots. At soil temperatures 65°-80° F the outside of roots is actively colonized by the fungus. It penetrates roots and has the root cortex colonized. It either kills or debilitates roots and provokes a decrease in water as well as nutrient uptake by the plant. By the way, plants with heavily damaged root systems have a greater chance to get injured or die, especially during periods of high temperature and drought stress. The symptoms usually don’t arise until July or August even although root colonization bursts out in May and lasts throughout the summer.

Necrotic ring spot treatment

NRS is still hard to handle due to its perennial nature as well as inconsistency in control with fungicides. However, a rational combination of cultural, chemical and genetic treatments can drastically tame NRS severity. When preparing a lawn, consider the following:

  • Resistance: A number of Kentucky bluegrass such as Midnight, Alpine, Apex, Adelphi, Award, Eclipse, Bristol, Classic, Liberator, Impact, Joy, Kelly, Miranda, Nugget, Mystic, Odyssey, Unique, NewStar, Wabash, P104, Washington and P105 are considered to be moderately resistant to this disease in limited field trials.
  • Thoroughly prepare site before seeding or sodding: The disease is more severe on sites with mediocre soil drainage and compacted soils. It’s crucial to properly prepare the soil before lawn establishment and to ensure the site is well drained.
  • Have diseased patches overseeded. Perennial ryegrass seed is capable of germinating fast. What’s more, it’s immune to this disease. The given plant can be successfully utilized to rapidly fill patches made by the disease. However, overseeding can’t prevent the intensification or development of the disease in other parts of your lawn.
  • You shouldn’t overwater: That’s probably the most crucial management practice for this disease. Many gardeners who have already faced NRS are prone to irrigating their lawns more frequently. Unfortunately, this way they only enhance this grass disease. You require watering your lawn to a depth of 6-8 inches and you should do it as infrequently as you can. Avoid doing it more than twice a week. Thus, you won’t create water stress for your plants. Your irrigation heads need to work in the right way. To avert puddles in your yard, you require limiting overlapping sprays.
  • Properly manage your established lawn: You require maintaining your turf at a height of about 2 ½-3 inches. Additionally, at any mowing don’t remove more than 1/3rd of the blade. Well, since its pathogen attacks the roots while neglecting the leaves, it means that it can’t be spread by mowing. Additionally, returning clippings with a mulching mower can really assist your grass to recover by simply recycling nitrogen at the stage of leaf decomposition. Keep in mind core aeration equipment is capable of spreading the NRS fungus.
  • Stay away from applying too much nitrogen fertilizers: The matter is that applications of over 4 lb total nitrogen per 1000 square feet every year can potentially enhance the disease. Moreover, the timing of fertilization is crucial too. You’d better stick with CSU tips for Kentucky bluegrass fertilization. You require applying most of the nitrogen exactly in the fall because spring fertilizer applications can be favorable for the disease.
  • Consult experts when it comes to fungicides or sulfur applications: It can really help, but it’s too complex to try handling it on your own, especially if you lack experience in chemical treatment.