Understanding Gray leaf spot disease in turf management

Managing grey leaf spot effectively requires understanding its causes, recognising early symptoms, and applying appropriate cultural and chemical controls.

Causes

Grey leaf spot thrives under specific environmental and turf management conditions. The main factors contributing to outbreaks include:

• Extended Humidity: Persistent high humidity creates a favourable environment for Pyricularia grisea.
• Warm Weather: The disease is most aggressive during warm periods, particularly when average daytime temperatures exceed 20°C.
• Turf Under Stress: Factors such as excessive nitrogen, low mowing heights, and thick thatch layers make turf more vulnerable.
• Thatch Build-Up: Thatch provides an ideal habitat for fungal spores to survive and germinate.

Identification

To effectively manage grey leaf spot, it is essential to identify its symptoms early:

• Initial Spots: Small, water-soaked spots on leaves that enlarge and turn greyish are early indicators.
• Twisting Leaves: Affected leaves often twist and curl, a hallmark of grey leaf spot.
• Rapid Deterioration: Infected areas can quickly decline, resulting in large patches of damaged turf.
• Grey Lesions: Lesions with a greyish colour and dark brown or purple edges are characteristic of this disease.

Cultural Management Strategies

Effective cultural practices can greatly reduce the severity and spread of grey leaf spot:

• Water Management:
  • Avoid over-watering and ensure proper drainage to keep soil moisture in check.
  • Water deeply but less frequently to encourage deeper root growth and minimise surface moisture.
• Enhance Airflow:
  • Trim surrounding vegetation and modify landscape features to improve airflow around the turf.
  • Use fans in enclosed areas to decrease humidity and help dry the turf canopy.
• Thatch Control:
  • Regularly aerate and dethatch to reduce organic matter where spores can thrive.
  • Apply sand topdressing to improve soil structure and drainage.
• Irrigation Timing:
  • Watering early in the morning helps the turf dry faster, reducing leaf wetness duration.
• Balanced Nutrition:
  • Maintain appropriate fertility levels to support healthy turf growth.
  • Avoid excessive nitrogen, which can exacerbate disease conditions.

Chemical Control

When cultural methods are insufficient, fungicides can provide effective control of grey leaf spot:

• Choosing Fungicides:
  • Use products specifically labelled for grey leaf spot, such as Ascernity and Instrata Elite.
  • Medallion can be used in rotation to prevent fungicide resistance.
  • Avoid Heritage in this situation.
• Timing Applications:
  • Preventative applications during high-risk periods are most effective.
  • Apply fungicides at the first sign of disease to quickly control outbreaks.
• Application Best Practices:
  • Ensure thorough coverage of both the turf canopy and root zone, as the pathogen can be present in both areas.
  • Follow the label instructions carefully regarding dosage, intervals, and application methods to achieve the best results.

Conclusion

By understanding the specific conditions that favour grey leaf spot, recognising its symptoms early, and employing both cultural and chemical controls effectively, turf managers can significantly mitigate the impact of this disease and maintain a healthy, resilient turf.