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Necrotic Ring Spot Disease

Definition: Necrotic ring spot disease is a common fungal disease that affects turfgrass, particularly in cool-season grasses such as Kentucky bluegrass and fine fescue. It is characterized by the formation of circular or ring-shaped patches of dead or dying grass in lawns.

Symptoms

Leaf Symptoms: The leaves within the affected patches initially turn yellow and then progress to a reddish-brown or bronze color. As the disease progresses, the leaves may wither and die, resulting in the formation of circular patches.

Root Symptoms: Necrotic ring spot disease primarily affects the roots of the grass. Infected roots exhibit dark brown or black lesions, which can lead to root rot and ultimately the death of the grass plants.

Causal Agent

Fungus: The primary causal agent of necrotic ring spot disease is the fungus Ophiosphaerella korrae. This fungus infects the roots of the grass and spreads through the soil, leading to the development of the characteristic circular patches.

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Conditions Favoring Disease Development

Moisture: Necrotic ring spot disease thrives in moist conditions, particularly when the soil is consistently wet. Overwatering or poor drainage can create an ideal environment for the fungus to grow and spread.

Temperature: The disease is most prevalent in cool and humid climates, with temperatures ranging from 60 to 75 degrees Fahrenheit (15 to 24 degrees Celsius). These conditions promote the growth and activity of the fungus.

Soil Compaction: Compacted soil restricts root growth and makes the grass more susceptible to infection. Poor soil aeration and compaction can contribute to the development and severity of necrotic ring spot disease.

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Management and Control

Cultural Practices: Implementing proper cultural practices can help prevent and manage necrotic ring spot disease. These include regular mowing at the appropriate height, proper watering techniques, and improving soil drainage through aeration and decompaction.

Fungicide Treatment: In severe cases, fungicide applications may be necessary to control the disease. Fungicides containing active ingredients such as azoxystrobin or propiconazole can be effective in suppressing the growth of the fungus.

Resistant Grass Varieties: Planting resistant grass varieties can help reduce the risk of necrotic ring spot disease. Certain cultivars of Kentucky bluegrass and fine fescue have shown resistance to the fungus and can withstand its attack.

Proper Fertilization: Maintaining a balanced fertility program can promote healthy grass growth and enhance the plant’s ability to resist diseases. Avoid excessive nitrogen fertilization, as it can increase the susceptibility of the grass to necrotic ring spot disease.

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Thatch Management: Regular dethatching can help prevent the buildup of excessive thatch, which can create an ideal environment for the fungus to thrive. Thatch removal promotes better air circulation and reduces the risk of disease development.

By implementing these management practices, homeowners and gardeners can effectively control and prevent the spread of necrotic ring spot disease, ensuring a healthy and vibrant lawn.

Keywords: disease, necrotic, fungus, patches, development, growth, circular, symptoms, conditions