Brown patch, caused by the fungal pathogen Rhizoctonia solani, is one of the most common disease problems encountered in tall fescue turf during the hot weather months.
How to Identify It
- The Symptoms (Visual Cues): Look for circular or irregular patches of blighted turf (tan, orangish brown) ranging from a few inches to several feet in diameter. On individual leaf blades, look for distinct tan lesions featuring dark brown borders.
- The Signs (Physical Pathogen): On humid, dewy mornings, you can often see cobwebby, white fungal growth (mycelium) resting on the grass canopy.
What Enhances Disease Severity?
Fungal outbreaks rely on the alignment of the “Disease Triangle:" A susceptible host, a virulent pathogen, and a conducive environment. Brown patch thrives on hot summer nights when air temperatures stay above 68°F, and leaves remain wet for more than 8 consecutive hours. Furthermore, brown patch is a “high-nitrogen” disease, meaning excessive nitrogen fertilization in your tall fescue turf right before or during hot, humid windows drastically amplifies its severity.
Cultural Practices to Prevent and Alleviate Brown Patch
Before reaching for a chemical solution (fungicide), adjust your management routine to break the disease triangle:
- Reduce Leaf Wetness: Only irrigate during the early morning hours (between 5:00 and 10:00 AM) so the canopy dries quickly during the day. Avoid watering in the evening, because it results in wet leaves all night.
- Improve Airflow: Trim low-hanging tree branches to maximize air movement, lowering localized relative humidity.
- Alleviate Plant Stress: Raise your mowing height to promote healthier plants with more photosynthesis (carbohydrate accumulation) and deeper roots. Relieve soil compaction through core aerification in the spring or fall in tall fescue turf.
- Smart Fertility & Seeding: Avoid summer nitrogen applications for tall fescue —fertilize in the fall instead. When repairing damaged areas in September, overseed with newer, improved tall fescue cultivars that possess better natural disease resistance.
Chemical Control: Active Ingredients
If your tall fescue turf has a chronic history of severe brown patch, a preventative strategy using systemic fungicides may be needed. Systemic products are absorbed into the plant to protect new growth for a longer period of time, whereas contact fungicides merely sit on the surface.
- When to Apply: Apply preventatively in early-to-mid June as humidity rises and night temperatures consistently exceed 60°F, repeating every 4 to 6 weeks through the summer may be needed, depending on disease pressure (environmental conditions). Curative applications only protect uninfected new growth; they cannot restore already dead tissue.
- Top Active Ingredients (Liquids are preferred for uniform canopy coverage):
Azoxystrobin, pyraclostrobin, trifloxystrobin, propiconazole, tebuconazole, fluoxastrobin, flutolanil, myclobutanil, some others.
This is an excellent guide – Chemical Control of Turfgrass Diseases 2024 by Univ. of Kentucky, Rutgers Univ., and the Univ. of Wisconsin-Madison.
Always read and follow all pesticide label directions to know what sites you can legally apply to and application rates. The label is the law.
Alicia Boor is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Extension. You can contact her by e-mail at aboor@ksu.edu or calling 620-793-1910.
K-State Extension is an equal opportunity employer and provider. Kansas State University, County Extension Councils, Extension Districts, and U.S. Department of Agriculture Cooperating.