Necrotic ringspot (NRS) is a perennial fungal disease primarily affecting Kentucky bluegrass. It causes distinct circular or doughnut-shaped patches of dead grass in lawns and turf.
Understanding Necrotic Ringspot (NRS)
NRS is a persistent problem because the fungus survives in the thatch and soil, re-emerging year after year.
Symptoms and Identification
- Appearance: The disease manifests as circular or ring-shaped patches of dead or dying grass, often with a green center, creating a "doughnut" appearance. Patch size can vary from a few inches to several feet in diameter.
- Timing: Symptoms are most noticeable in late July and August, during periods of heat stress.
- Affected Grass: Primarily affects Kentucky bluegrass but can also occur on other cool-season grasses.
- Root Rot: NRS is characterized by a dark brown to black discoloration and rot of the roots and rhizomes.
Management and Control
Controlling NRS requires a multi-pronged approach:
- Good Turf Management Practices:
- Proper Watering: Avoid frequent, shallow watering. Water deeply and infrequently to encourage deep root growth.
- Fertilization: Maintain adequate soil fertility, but avoid excessive nitrogen fertilization, especially in the spring.
- Thatch Management: Reduce thatch accumulation through core aeration and dethatching. Thatch provides a favorable environment for the NRS fungus.
- Overseeding: Overseed affected areas with resistant varieties of Kentucky bluegrass or other grass species.
- Fungicide Applications:
- Preventative Applications: Apply systemic fungicides preventatively in the spring or early summer before symptoms appear.
- Curative Applications: Fungicides can be used to suppress the disease, but they are most effective when applied early in the disease cycle. Multiple applications may be needed. Consult a professional for fungicide recommendations.
Recovery
Although NRS can cause significant damage, affected areas often recover in the fall and spring as temperatures cool and moisture increases. However, without proper management, the disease will likely return the following year.
