Brown patch is a common and destructive lawn disease, particularly challenging during the summer months. This fungal infection is caused by the soil-borne pathogen Rhizoctonia solani, which thrives in specific environmental conditions. It typically develops when nighttime temperatures are consistently above 68°F and daytime temperatures exceed 80°F, coupled with high humidity and prolonged leaf wetness. Identifying this disease and implementing timely management strategies is the first step toward restoring turf health. The best approach involves immediate cultural adjustments, careful use of chemical controls, and long-term preventative care.
Confirming the Diagnosis: Identifying Brown Patch
Identifying brown patch correctly is paramount, as other lawn issues can mimic its appearance. The disease manifests as roughly circular patches of thinned, light brown grass, ranging from a few inches to several feet in diameter. Often, the center of the patch may appear to recover, creating a distinct “doughnut” or ring shape.
A hallmark sign is the presence of a dark, grayish-purple border surrounding the patch, commonly referred to as a “smoke ring.” This ring indicates the fungus is actively growing and is most apparent on close-cut grass, frequently fading by midday. When inspecting individual grass blades, look for tan, irregular lesions with dark brown margins. The disease primarily attacks the leaf blades and sheaths, often leaving the crown and base of the grass plant green and intact.
Immediate Cultural Control Strategies
Addressing environmental factors is the most effective immediate action to halt the spread of brown patch. Since the fungus requires extended periods of leaf wetness to infect, adjusting your watering schedule is the most important change. Cease all evening or late afternoon watering, as this allows the foliage to remain wet overnight when the fungus is most active. Instead, switch to deep, infrequent watering cycles conducted early in the morning, ideally before 10 AM, to ensure grass blades dry quickly as the sun rises.
Adjusting mowing practices is also an immediate response to minimize disease transmission. Temporarily increase your mowing height, as shorter turf can be more susceptible to severe damage. During an outbreak, bag and remove clippings from the infected areas, preventing the mechanical spread of fungal mycelium to healthy parts of the lawn. Additionally, limit foot traffic across the affected areas to avoid transferring the soil-borne pathogen.
Improving air circulation and light penetration is another non-chemical method to dry the turf surface faster. Pruning lower limbs of nearby shrubs or trees can increase the amount of sunlight reaching the lawn. Better airflow helps to evaporate moisture and reduce the humidity level directly surrounding the grass plants. Good surface and soil drainage also contribute significantly to reducing prolonged leaf wetness.
When and How to Apply Fungicides
Fungicides are typically reserved for severe, recurring cases or for high-value turf areas where cultural controls alone are insufficient. When applying a chemical treatment, the timing is crucial. Applications are generally more effective when used preventatively before symptoms appear, or curatively at the immediate onset of the disease. Fungicide applications are especially justified when weather forecasts predict prolonged hot and humid conditions favorable for disease development.
Fungicides are broadly categorized into two types. Contact fungicides remain on the surface, creating a protective barrier that kills fungal spores upon contact. These treatments are short-lived and require frequent reapplication, especially after rain or mowing, because they do not move into new growth. Systemic fungicides are absorbed into the plant tissue and translocate upward through the vascular system, offering longer-lasting protection.
Systemic products, such as those containing active ingredients like propiconazole or azoxystrobin, are often preferred for curative control due to their residual effects, lasting up to 28 days. It is important to strictly follow the manufacturer’s label instructions regarding application rates, intervals, and safety precautions. To prevent the fungus from developing resistance, alternate between different chemical classes of fungicides.
Long-Term Lawn Management to Prevent Recurrence
Preventative measures focus on modifying the lawn environment to make it less hospitable to Rhizoctonia solani. The fertilization schedule is a major factor in brown patch susceptibility. Avoid applying high-nitrogen fertilizers during the summer months when heat and humidity are high, as this encourages the lush, soft leaf growth that the fungus readily attacks. Instead, shift the majority of nitrogen applications to the fall and early spring, using a slow-release source during the summer if feeding is necessary.
Addressing soil health improves the lawn’s resilience. Core aeration reduces soil compaction and helps to improve water infiltration and drainage, preventing standing water. Dethatching removes excessive layers of organic material where the fungus can survive and multiply. These mechanical processes should be performed during the cooler seasons to avoid stressing the turf during an active disease period.
Ensuring the proper soil chemistry supports robust turf growth and defense mechanisms. Performing a soil test helps determine the lawn’s pH level and nutrient balance, including phosphorus and potassium. Correcting nutrient deficiencies or adjusting a highly acidic or alkaline pH can significantly enhance the grass plant’s natural ability to withstand disease pressure. Selecting turfgrass varieties known for their resistance to brown patch is a foundational long-term preventative step.