Necrotic Ring Spots vs Fairy Rings – What’s the difference?

Necrotic Ring Spot (NRS) is a common turfgrass disease that primarily affects lawns, particularly in temperate regions. Characterised by distinct circular patches of dead or dying grass, it can be frustrating for homeowners and turf managers alike.

This article will address the most frequently asked questions about Necrotic Ring Spot, providing insights into its causes, symptoms, prevention, and treatment.

Difference Between Necrotic Ring Spots and Fairy Rings

Necrotic Ring Spot (NRS) and Fairy Rings are both turfgrass diseases that cause circular patches on lawns, but they differ significantly in their causes, appearance, and management.

Necrotic Ring Spot is caused by the fungus Ophiosphaerella korrae. It primarily affects cool-season grasses like Kentucky bluegrass, creating circular or ring-shaped patches of dead grass with a possible green centre.

The disease often results from stress factors like poor soil aeration, over-fertilisation, and drought. NRS damages the grass roots, leading to poor water and nutrient uptake, and usually appears in spring and autumn.

Fairy Rings, on the other hand, are caused by various soil-dwelling fungi that decompose organic matter. They create rings of lush, dark green grass, often accompanied by mushrooms or a dry, dead patch in the middle.

Fairy Rings can appear on all types of turf and are more noticeable during wet weather. The fungi in Fairy Rings do not directly attack the grass but rather alter soil conditions, leading to either excessive growth or death of the grass.

Comparison Table: Necrotic Ring Spots vs. Fairy Rings

What is Necrotic Ring Spot?

Necrotic Ring Spot is a fungal disease caused by Ophiosphaerella korrae, a pathogen that primarily attacks cool-season grasses such as Kentucky bluegrass. The disease is named for the circular or ring-shaped patches of dead grass it produces, often with a healthy green centre, giving the affected area a “frog-eye” appearance. The patches typically range from a few inches to several feet in diameter.

How Does Necrotic Ring Spot Develop?

The fungus responsible for NRS thrives in soil, particularly under conditions that stress the grass, such as drought, poor soil aeration, and over-fertilisation with nitrogen. The disease is most active in the cooler, wetter months of spring and autumn, although the damage may become more visible during the heat of summer when the grass is under greater stress.

The fungus infects the grass by attacking the roots, leading to poor water and nutrient uptake. Over time, this weakens the grass, causing it to die off in patches. The disease can persist in the soil for several years, making it a recurring problem if not properly managed.

What are the Symptoms of Necrotic Ring Spot?

The primary symptom of Necrotic Ring Spot is the appearance of circular or irregular patches of dead or dying grass. These patches often have a distinct yellow or straw-coloured hue, surrounded by a border of darker, healthy-looking grass. As the disease progresses, the patches may expand and merge, creating larger areas of damaged turf.

In the early stages, the affected grass may appear wilted or stunted, with a reduction in root mass. This is often more noticeable during periods of heat or drought, as the weakened roots struggle to provide adequate moisture to the plant. Over time, the patches can become more prominent, especially if the disease is not addressed.

How Can Necrotic Ring Spot Be Prevented?

Preventing Necrotic Ring Spot involves a combination of cultural practices aimed at maintaining healthy, stress-resistant turf. Some key prevention strategies include:

• Proper Watering: Water deeply and infrequently, ensuring that the soil is moist to a depth of 6-8 inches. Avoid watering in the late afternoon or evening, as prolonged leaf wetness can encourage fungal growth.
• Aeration: Regularly aerate the soil to improve water and nutrient penetration and reduce compaction. This helps to create an environment less conducive to fungal growth.
• Fertilisation: Avoid over-fertilising with nitrogen, especially in the spring. Instead, use a balanced fertiliser that provides adequate potassium and phosphorus, which help strengthen the roots and improve disease resistance.
• Mowing: Keep your grass at a height of around 2.5 to 3 inches. Mowing too short can stress the grass and make it more susceptible to disease.
• Overseeding: Regularly overseed your lawn with disease-resistant grass varieties to improve turf density and reduce the spread of the fungus.

How is Necrotic Ring Spot Treated?

Once Necrotic Ring Spot has taken hold, treatment can be challenging, but it is not impossible. The following steps can help manage and reduce the impact of the disease:

• Fungicides: While fungicides can help control NRS, they are most effective when applied preventatively or at the first sign of symptoms. Common fungicides used include azoxystrobin, propiconazole, and myclobutanil. It is important to follow the manufacturer’s instructions and rotate fungicides to prevent resistance.
• Cultural Practices: Continue with the cultural practices outlined above, focusing on reducing stress on the grass. Proper watering, aeration, and fertilisation are crucial in helping the grass recover.
• Topdressing: Applying a light layer of topsoil or compost can help improve soil structure and promote healthier root growth. This can also help to suppress the fungal spores in the soil.
• Reseeding: If large areas of the lawn are affected, it may be necessary to reseed with disease-resistant varieties. This can help to restore the lawn’s appearance and reduce the likelihood of future outbreaks.

Is Necrotic Ring Spot a Permanent Problem?

While Necrotic Ring Spot can be persistent, it is not necessarily a permanent problem. With proper management and care, it is possible to reduce the severity of the disease and restore the health of your lawn. However, it is important to remain vigilant, as the fungus can remain dormant in the soil and reappear when conditions are favourable.

Consistent maintenance, including proper watering, aeration, and fertilisation, is key to keeping your lawn healthy and resistant to disease. By following the prevention and treatment strategies outlined in this article, you can successfully manage Necrotic Ring Spot and enjoy a lush, green lawn.

Table: Summary of Necrotic Ring Spot Management

By understanding the nature of Necrotic Ring Spot and implementing these strategies, you can protect your lawn from this troublesome disease and maintain a healthy, vibrant turf.