How to Prevent Large Patch Disease

What Is Large Patch Disease

Large patch (Rhizoctonia solani) is a fungal disease that affects warm-season grasses including bermuda, zoysia, centipede, and St. Augustine. It is often mistakenly called brown patch, but brown patch is a different disease that targets cool-season grasses. In Middle Georgia, large patch is the correct diagnosis. The fungus attacks the leaf sheath at the soil level, causing circular patches of yellowing and thinning grass that can range from a few feet to several yards across.

When Large Patch Is Most Active

Large patch is most active when soil temperatures are between 50 and 70 degrees Fahrenheit — which means fall and spring in Middle Georgia. The disease actually starts in fall, progresses through winter, and continues into spring before going dormant in summer heat. Many homeowners first notice it in spring when grass greens up everywhere except the affected patches.

• Fall and spring are peak infection periods in Middle Georgia.
• Soil temps between 50 and 70 degrees combined with moisture trigger outbreaks.
• The disease goes dormant in summer when soil temperatures exceed 80 degrees.

Cultural Prevention Practices

The best prevention is reducing conditions that favor the fungus. Avoid excess nitrogen in fall — it creates tender growth that the fungus exploits. Improve drainage in areas where water pools. Reduce thatch buildup through aeration. Water in the morning so grass dries before evening. Avoid mowing wet grass and clean mower blades between sections to prevent spreading spores.

• Reduce fall nitrogen applications.
• Improve soil drainage and reduce thatch through core aeration.
• Water early in the morning, never in the evening.
• Clean mower blades between affected and healthy areas.

Fungicide Treatment Options

Preventive fungicide applications in September and again in October are far more effective than treating active infections. Products containing azoxystrobin or propiconazole target the Rhizoctonia fungus directly. Curative applications can slow the spread but cannot reverse existing damage. Affected areas typically fill back in once the grass resumes active growth in spring or summer.