Necrotic ring spot

Necrotic ring spot is a devastating fungal disease of turfgrass caused by the pathogen Ophiosphaerella korrae. This fungus specifically targets the root and crown systems of various cool-season grass species, causing significant decay and the eventual death of the turf in localized areas.

The primary hosts of this pathogen are Kentucky bluegrass and fine fescues. In landscape settings, these grasses are highly valued for their texture, but they remain susceptible to the stress induced by the fungus, which disrupts their ability to uptake water and nutrients effectively.

Symptoms typically manifest as small, chlorotic patches that expand over time into ring-shaped patterns. As the infection progresses, the grass within the affected area turns a straw-like color. Often, healthy grass may reappear in the center of the ring, creating a distinctive 'frog-eye' appearance that is highly characteristic of the disease.

The fungus thrives in environmental conditions characterized by cool, wet springs and autumns. Poor drainage, soil compaction, and excessive thatch accumulation provide the perfect environment for the pathogen to persist in the soil and infect new root tissue during periods of active growth.

Effective management requires an integrated approach to turf health. Recommended practices include:

• Reducing thatch through mechanical dethatching.
• Implementing regular core aeration to improve soil oxygen levels.
• Adjusting irrigation schedules to avoid prolonged soil saturation.
• Applying systemic fungicides during peak infection periods as identified by local extension services.