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Necrotic Ring Spot

Causal Agent: Ophiosphaerella korrae formerly known as Leptosphaeria korrae

 

Susceptible Turfgrass
Kentucky Bluegrass, Annual Bluegrass, Rough Bluegrass, fine-leaf Fescue.

 

Symptoms

  • Necrotic ring spot first appears as small light green spots and progresses to thinned, circular patches that are yellow to light-green in colour and approximately 8 to 40 cm in diameter.

  • The patches, which can expand up to 1 metre in diameter, eventually turn brown or straw-coloured and die.

  • The roots and rhizomes of the affected turfgrass turn brown to black. Grass plants can survive and recolonise the centre of the patches, which leads to a ring-like appearance.

 

Conditions favouring Disease

  • Necrotic ring spot initiates in moist soil, thrives in temperatures of up to 27°C and becomes more severe in higher temperatures and drought conditions.

  • Seeded sites, as well as sodded sites in newly cleared woodlands, are susceptible to this disease.

  • It is also found in areas with compacted soil and that are high in nitrogen during the Spring and Summer.

 

Integrated Turf Management

  • Raise mower height.

  • Reduce soil compaction through aerification and use of lightweight equipment.

  • Use moderate to high amounts of phosphorous and potash.

  • Maintain adequate nitrogen and a balanced fertility.

  • Minimise the amount of shade.

  • Lightly irrigate (approximately 2.5 mm) in the mid-afternoon on a daily basis to cool plants.

  • Avoid drought stress.

  • Top-dress and aerate turf as needed.

  • Reduce thatch.

  • Overseed with Perennial Ryegrass or more tolerant Bluegrass cultivars.

  • Apply penetrant fungicides on a preventive basis.

 

Fungicidal Control
Heritage has a label recommendation for Necrotic Ring Spot in South Africa.