Brown Patch is a common lawn disease affecting turfgrass, particularly during warm, humid conditions. It is caused by the soil-borne fungus Rhizoctonia solani, which thrives when temperatures are high and the lawn remains wet for extended periods. The fungus attacks the grass blades, leading to rapid decline and unsightly damage. Eliminating Brown Patch requires a two-pronged approach: immediate chemical intervention to halt the disease’s progression, followed by long-term adjustments to lawn maintenance practices.
Identifying Brown Patch Symptoms
Identifying Brown Patch is crucial for effective treatment, as its appearance can be confused with other lawn issues. The disease typically manifests as roughly circular patches of damaged grass, ranging from a few inches up to several feet in diameter. These patches often look sunken or matted, and the grass inside is usually brown or straw-colored.
A specific sign of active Brown Patch is the “smoke ring,” a grayish-dark border visible around the perimeter of the patch. This border is the actively advancing margin of the fungus, best observed in the early morning when dew is present. On susceptible wide-bladed grasses like tall fescue or perennial ryegrass, individual leaf blades may exhibit distinct lesions. These lesions have tan or light brown centers surrounded by a dark brown or black margin, often called sheath rot.
Applying Fungicide Treatments
Fungicides stop an active Brown Patch infection and are categorized as either curative or preventative. Curative fungicides halt an existing outbreak and typically contain systemic active ingredients like Propiconazole. These products stop the immediate spread of the fungus but may require higher application rates to treat an established infection.
Preventative fungicides are used before the disease appears, generally when nighttime temperatures remain above 60°F to 70°F. Ingredients such as Azoxystrobin are excellent for preventative control due to their long residual activity. For severe or recurring infections, a combination of active ingredients is often recommended to broaden control and mitigate the risk of resistance.
Follow the manufacturer’s label instructions precisely regarding application rate and reapplication interval. Applying the fungicide at the first sign of symptoms provides the best chance of recovery, as susceptible grasses struggle to recover during summer heat. Proper application technique, ensuring adequate coverage, is essential for effectiveness.
Preventing Recurrence Through Cultural Practices
Managing Brown Patch requires modifying the lawn environment to be less hospitable to the fungus. The most important change is irrigation timing, as the fungus requires grass blades to be wet for 10 to 12 hours for infection. Water the lawn deeply and infrequently only in the early morning (6:00 AM to 10:00 AM) so the sun can quickly dry the foliage. Avoid watering in the late afternoon or evening, which extends leaf wetness throughout the cool night.
Mowing practices play a significant role in prevention and disease spread. Keep mower blades sharp to produce a clean cut, minimizing torn edges that provide entry points for fungal spores. Increase the mowing height during summer months to help the turf become more resilient to environmental stresses. Avoid mowing affected areas when the grass is wet, as this mechanical action can easily spread the fungal mycelium.
Adjust fertilization habits to suppress the fungus, which favors the lush growth promoted by high nitrogen levels. During the hot, humid summer when Brown Patch is most active, avoid applying high-nitrogen fertilizers. Focus nitrogen applications on cooler spring and fall months, and ensure the soil has adequate levels of potassium and phosphorus based on a soil test.
Managing soil structure and health is a major component of prevention. The fungus thrives in poorly drained or compacted soils with excessive thatch, which holds moisture. Aerating the lawn once a year reduces soil compaction and improves air circulation and water infiltration. Dethatching is also beneficial for reducing the thick layer of organic debris where the fungus survives.