Grey Leaf Spot in St. Augustine Grass: What You Need to Know

Overview

Grey leaf spot is a fungal disease that primarily affects St. Augustine grass but can also infect bermudagrass and centipede grass. This disease thrives in warm, humid conditions and can cause significant damage to your lawn if left untreated.

Symptoms

Identifying grey leaf spot early is crucial for effective management. Here’s what to look for:

• Initial Appearance: Small, brown leaf spots that expand into large, oval, or elongated tan-to-gray spots with purple or brown borders. Some spots may have a yellow halo or cause general leaf yellowing.
• Progression: In warm, humid conditions, the fungus produces a grayish mycelium, turning spots gray and fuzzy. Affected blades wither and die, leading to significant turf damage and a brown cast to the lawn.

Recognizing these symptoms early can prevent extensive lawn damage and help you take prompt action.

Development Factors

Understanding the conditions that promote grey leaf spot development can aid in its prevention:

• Susceptibility: St. Augustine grass is the most commonly affected, although bermudagrass and centipede grass can also be infected.
• Active Period: The disease is most active from June through August.
• Optimal Conditions: Grey leaf spot develops between 77-86°F during the day and above 65°F at night. It requires at least 14 hours of continuous leaf wetness, with high humidity and improper irrigation increasing susceptibility. Excessive nitrogen fertilization also promotes disease development.

By monitoring these conditions, you can anticipate and mitigate the risk of grey leaf spot in your lawn.

Cultural Control

Implementing proper lawn care practices can significantly reduce the risk of grey leaf spot:

• Leaf Wetness Management: Schedule irrigation early in the morning to ensure quick drying of foliage. Prune or remove trees, shrubs, or other barriers to improve air movement and sunlight penetration.
• Mowing Practices: Mow frequently during the summer to remove excess leaf tissue, keep the canopy open and dry, and remove developing grey leaf spot lesions. Collect and dispose of clippings when disease symptoms are present to reduce spread.
• Fertilization: Apply nitrogen and other nutrients as recommended to maintain vigorous growth during the summer, but avoid excessive nitrogen. Ensure proper mowing and irrigation practices to minimize stress and disease risk. For expert fertilization services, visit our fertilization services page.

These cultural control methods create an environment less conducive to grey leaf spot, helping maintain a healthy lawn.

Management Tips

Effective management of grey leaf spot involves several key practices:

• Thatch Reduction: Maintain a minimal thatch layer to reduce disease habitat.
• Irrigation: Deep, infrequent watering (once per week with one inch of water) early in the morning to promote quick drying of the foliage.
• Avoid Weed Killers: Do not use post-emergent weed killers while the disease is active. For more tips, check out our weed control services.
• Air Circulation and Light: Improve by pruning overhanging trees and nearby shrubs.
• Mowing: Mow at the proper height, only when the grass is dry, and bag clippings if disease is present. Learn more about our lawn mowing service.
• Chinch Bug Control: Manage infestations to reduce stress on the grass.
• Fungicides: Use as needed, along with proper turfgrass culture practices. Fungicides should be applied preventatively, especially in mid-June to early July, with repeated applications every 14 to 21 days. Rotate fungicides to prevent resistance.

By following these management tips, you can effectively control grey leaf spot and maintain a healthy lawn.

Chemical Control

For severe grey leaf spot infestations, chemical control may be necessary. Here are some effective fungicides:

• Fluoxastrobin: Excellent effectiveness. Example: Fame Granular Fungicide
• Azoxystrobin: Good effectiveness. Examples include Heritage G, Scott’s Disease EX, Headway G, Quali-Pro Strobe ProG
• Pyraclostrobin: Good effectiveness. Example: Pillar G Intrinsic Fungicide
• Thiophanate Methyl: Good effectiveness. Example: Bonide Infuse Systemic Disease Control Lawn & Landscape
• Propiconazole: Fair effectiveness. Examples include Bayer BioAdvanced Fungus Control for Lawns RTS2, Bayer BioAdvanced Fungus Control for Lawns Ready to Spread Granules II
• Myclobutanil: Fair effectiveness. Examples include Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate, Monterey Fungi-Max Multi-purpose Fungicide Concentrate

When using chemical controls, always follow the label directions for the best results and to ensure the safety of your lawn and the environment.

Conclusion

Grey leaf spot in St. Augustine grass can be a challenging problem, but with the right knowledge and practices, it is manageable. By understanding the symptoms, development factors, and implementing effective cultural and chemical control methods, you can keep your lawn healthy and beautiful. If you need expert assistance, don’t hesitate to contact us or fill out our estimate request form. Our team is here to help you achieve the lush, green lawn you desire. For comprehensive lawn and landscape maintenance, visit our lawn and landscape maintenance page.