Necrotic ring spot is a common and destructive fungal disease that affects turfgrass, causing circular and irregular patches of dead, brown grass surrounded by healthy green turf. The disease is particularly devastating because it attacks your lawn's root system, making it one of the most damaging lawn diseases homeowners may encounter. Keep reading to learn how to identify and deal with necrotic ring spot!
The disease is caused by the soilborne fungus Ophiosphaerella korrae. It primarily affects cool-season grasses such as Kentucky bluegrass, annual bluegrass, and fine fescue. If untreated, necrotic ring spot can persist for years, wreaking havoc on your lawn’s health and aesthetics.
Necrotic ring spot typically appears as circular patches of dead grass that are straw-colored or light brown. These patches often have a characteristic ring shape, with the center of the patch sometimes recovering or appearing healthy. This creates a "frog-eye" pattern, which is the key identifier of the disease. It’s important to inspect your lawn closely during peak periods of activity to not mistake necrotic ring spot for other lawn problems, such as grub damage or nutrient deficiencies.
How To Identify Necrotic Ring Spot
Ophiosphaerella korrae lives in the soil and infects grass roots, especially where nitrogen levels are low. The fungus thrives in cool, moist conditions and becomes active in the spring and fall. Kentucky bluegrass is particularly vulnerable to necrotic ring spot due to its shallow root system and dense growth habit, which creates a favorable environment for the fungus.
Thatch buildup is one of the most common causes of necrotic ring spot. Excessive thatch provides a haven for the fungus by retaining moisture and reducing air circulation. Thatch layers thicker than half an inch provide a haven for the fungal spores and lead to soil compaction, which creates conditions where water and nutrients cannot penetrate effectively. This weakens the grass, making it more susceptible to infection.
Main Causes
Watering and fertilizing your lawn too much in an attempt to combat the disease will actually make the problem much worse. Overwatering or inconsistent watering schedules can stress the lawn and encourage fungal growth. Excessive nitrogen fertilization promotes lush, top-heavy grass growth at the expense of healthy roots, increasing the risk of infection and producing more thatch. It is always best to consult with a professional once signs of infection are present.
Necrotic ring spot spreads through a combination of fungal growth and environmental factors. The fungus lives in the soil and on grass blades, and its spores can spread through wind, water runoff, or movement of contaminated soil during landscaping activities. This means that even healthy grass adjacent to infected areas is at risk, especially in colder months. Wet, cool weather in spring and fall provides the ideal environment for fungal spores to germinate and infect new areas of turf.
In addition to environmental factors, necrotic ring spot spreads its infestation through tools and equipment, such as aerators, mowers, or shovels that can carry infected soil or grass clippings to unaffected parts of the lawn. Even something as seemingly innocuous as foot traffic and pets can inadvertently spread the fungus by carrying spores from infected areas to healthy turf. It is important to always stay mindful of and avoid areas of infected grass until treatment can be administered.
Necrotic ring spot is a serious threat to your lawn that can kill your grass if the outbreak is severe. Unlike the more common foliar lawn diseases, this fungal infection damages the root system, which weakens the grass and prevents it from thriving. If left untreated, the grass in the affected areas will be unable to absorb nutrients and will eventually die, leaving unsightly patches of bare soil.
One of the most frustrating aspects of necrotic ring spot is its persistence. The fungus can survive in the soil for years, even when the grass appears healthy, meaning that the disease can reappear under favorable conditions, causing recurring damage. Necrotic ring spot can also create an environment that invites secondary issues, such as weed infestations and soil erosion.
Necrotic ring spot is challenging to manage, but a combination of proactive prevention and targeted treatment can help restore your lawn’s health. Turf diseases that affect the roots and crowns of your lawn must be dealt with promptly, as the damage they cause can be permanent and result in costly and time-consuming repairs. Consider the tips below if you see signs of necrotic ring spot in your lawn, or if you want to take measures to prevent this disease from appearing in the first place!
