Brown patch on bentgrass presents one of the most persistent challenges for turf managers maintaining high-quality putting surfaces and athletic fields. This destructive disease, caused primarily by the fungus Rhizoctonia solani, thrives in the dense, humid microclimate that bentgrass cultivars so expertly produce. Unlike superficial turf ailments, brown patch can rapidly progress from initial circular spots to large, irregular dead zones if not managed with precision and understanding.
Understanding the Pathogen and Disease Cycle
The agent responsible for brown patch, Rhizoctonia solani, is a soil-borne pathogen that exists as a complex of multiple anastomosis groups (AGs), with specific AGs showing preferences for certain turf species. The fungus survives the dormant season within infected plant debris and soil, making initial sanitation efforts critical for long-term control. Environmental triggers are essential; the pathogen requires extended leaf wetness, often from dew or irrigation, coupled with warm nighttime temperatures between 70°F and 90°F to initiate infection.
Identification and Diagnostic Symptoms
Accurate identification begins with observing the distinct visual patterns the disease creates on the turf canopy. Early symptoms manifest as small, water-soaked spots that quickly expand into large, circular to irregular patches ranging from a few inches to several feet in diameter. The characteristic color progression starts with a yellowish to bronze hue before transitioning to a definitive dark brown, giving the patch its namesake appearance.
Distinctive Turf Response
Unlike many foliar diseases, brown patch often causes significant internal crown and root rot in bentgrass, particularly under prolonged moisture. This systemic invasion leads to a characteristic softening of the turf mat and a slimy, foul-smelling odor when affected blades are pulled. The lesions on individual leaves are typically tan with a reddish-brown border, and a distinct grayish fungal mycelium may be visible on the grass blades during early morning dew.
Environmental and Cultural Factors
While the pathogen is necessary for disease development, the severity of an outbreak is heavily dictated by cultural practices and microclimate management. Over-fertilization with nitrogen, especially with quick-release forms, promotes lush, succulent growth that is highly susceptible to infection. Similarly, compaction and poor air circulation create the humid conditions the pathogen requires to flourish.
Excessive Nitrogen: High nitrogen levels increase leaf succulence and moisture content, providing an ideal nutrient source for the fungus.
Improper Mowing: Mowing grass too short or dull blades create wounds that facilitate entry points for the pathogen.
Irrigation Practices: Frequent, light watering fails to penetrate the root zone and keeps the canopy wet for extended periods.
Strategic Management and Control Tactics
Effective management of brown patch requires an integrated approach that combines cultural adjustments with targeted chemical applications. The cornerstone of cultural control is improving surface drainage and air movement; this can be achieved through vertical mowing, topdressing, and strategic pruning of surrounding vegetation. Adjusting the irrigation schedule to water deeply and infrequently, preferably in the early morning, allows the canopy to dry quickly during the day.
Chemical and Biological Options
Fungicide applications remain a critical tool for protecting high-value turf during periods of high disease pressure. Modern turf management utilizes a strategic rotation of fungicide classes, including demethylation inhibitors (DMIs) and succinate dehydrogenase inhibitors (SDHIs), to prevent the development of resistance. For organic management, products containing potassium bicarbonate or specific biofungicides can offer suppression, though they often require more frequent application and are less curative than synthetic options.
