Managing Diseases of Tall Fescue
Brown Patch General Information
A number of diseases can cause serious damage to tall fescue grown for landscapes, athletic fields, and other recreational areas. Other problems that resemble disease are caused by management and/or environmental factors. Accurate diagnosis is the key to successful management of diseases and other problems in turfgrasses. This publication reviews the diagnosis and management of the most common diseases in tall fescue landscapes.
Turf that is stressed or poorly managed is more susceptible to disease than grass that is healthy and well managed. Tall fescue is a cool-season grass that grows best in the spring and fall, and is stressed and weak during the summer months. Therefore, the most severe diseases of tall fescue occur during the summer when this grass is suffering from heat and drought stress.
The most destructive tall fescue diseases, brown patch and Pythium blight, are encouraged by wet, compacted soils. Proper design and construction of landscapes and athletic fields is very important for long-term management of these diseases. Avoid establishing turf in low lying areas that tend to collect water. Athletic fields should be crowned, with at least a 1% slope in one direction, to encourage the flow of water across the turf surface, and subsurface drainage should be installed to move water away from the field after it drains through the soil.
Prior to seeding of tall fescue, the soil should be tilled to a depth of 6" to 8" to eliminate any hard pans in the root zone. Following establishment, regular cultivation of landscapes and athletic fields is also necessary to alleviate soil compaction and maintain adequate drainage. The frequency of aerification that is needed depends on the intensity of use. Low-use areas should be aerified once per year, ideally in the fall. More heavily trafficked areas should be aerified at least twice, once in the spring and once in the fall.
Most tall fescue diseases are also encouraged by excessive shade. Tall fescue has very low shade tolerance and should not be planted in areas that receive less than 6 hours of full sun exposure per day. The fine-leaved fescues, such as hard fescue and strong creeping red fescue, perform well in shady areas and are very resistant to most turf diseases.
Brown patch is the most common and damaging disease of tall fescue in the southeastern United States. The symptoms of brown patch are roughly circular patches that are brown, tan, or yellow in color, ranging from 6 inches to several feet in diameter (Figure 1). The affected leaves typically remain upright, and lesions are evident on the leaves which are tan in color, have a dark brown border, and are irregular in shape (Figure 2). When the leaves are wet or humidity is high, small amounts of gray cottony growth, called mycelium, may be seen growing amongst affected leaves in the turf canopy.
Brown patch is most severe during extended periods of hot, humid weather. The disease can begin to develop when night temperatures exceed 60°F, but is most severe when low and high temperatures are above 70°F and 90°F, respectively. Brown patch also requires at least 10 to 12 hours of continuous leaf wetness in order to develop. Poor soil drainage, lack of air movement, shade, cloudy weather, heavy dew, over-watering, and watering in late afternoon favor prolonged leaf wetness and increased disease severity. Brown patch is particularly severe in turf that has been fertilized with excessive nitrogen. Inadequate levels of phosphorus and potassium have also been shown to contribute to injury from this disease.
Varieties of tall fescue vary widely in their susceptibility to brown patch. Selection of a tall fescue variety with a high level of brown patch resistance is a critical first step in any management program. Current lists of varieties with good brown patch resistance that perform well in North Carolina can be obtained from NC State's Turffiles Website ("http://www.turffiles.ncsu.edu/) or the National Turfgrass Evaluation Program (http://www.ntep.org/).
High levels of available nitrogen favor the spread of brown patch. Nitrogen induces tall fescue to produce soft, lush leaf tissue that is easily infected by the brown patch pathogen. Excessive foliar growth also results in a dense canopy that holds moisture and humidity for extended periods of time.
In general, tall fescue should not be fertilized with nitrogen in late spring or summer so as to discourage brown patch development. Following this type of program will result in yellowing and thinning of tall fescue during the summer as nitrogen is depleted from the soil. Turf in this condition is very resistant to brown patch, but may not be acceptable from an aesthetic standpoint. If fungicides are used to protect tall fescue from brown patch, then application of small amounts of slow-release nitrogen (= 0.25 lb N/1000 ft2/month) during the summer can help improve the quality of tall fescue turf. This practice, however, will encourage the development of other diseases, such as gray leaf spot and Pythium blight. Tall fescue that is fertilized during the summer should be monitored frequently for these diseases so that they may be controlled before widespread damage occurs.
Avoiding prolonged periods of leaf wetness will drastically reduce the severity of brown patch. Leaf wetness can originate from either irrigation or dew. To minimize leaf wetness, do not irrigate the turf on a daily basis. Instead, water deep and infrequent, every 3 to 4 days to a depth of 6 to 8 inches. The timing of irrigation is also critical; it is best to irrigate early in the morning, just before sunrise. This removes large droplets of dew and guttation water from the leaves and speeds drying of the foliage after sunrise. Avoid watering after sunrise or in the late afternoon/evening, as this will increase the duration of leaf wetness. For intensely managed athletic fields, daily removal of morning dew can help to reduce leaf wetness duration and minimize brown patch development. This can be accomplished by mowing, dragging a hose or rope over the turf, or running the irrigation system for a short time.
Brown patch is particularly severe in soils that are wet and compacted. Providing adequate surface and subsurface drainage, and minimizing compaction through regular aerification, will help to minimize the development of this disease.
Fungicides are effective for brown patch control, and can be applied on a preventative or curative basis. Fungicides vary widely in residual control, or the number of days of brown patch control after application. Fungicides containing the active ingredients azoxystrobin (Heritage 50WG, 0.2 oz/1000 ft2), pyraclostrobin (Insignia, 0.7 oz/1000 ft2) or flutolanil (Prostar 70WP, 2.25 oz/1000 ft2; Systar 80WDG, 3 oz/1000 ft2) consistently provide 28 days of brown patch control, even under severe conditions. For homeowner applications, products containing the thiophanate-methyl are sold under various brand names at garden stores and provide good brown patch control, but these products must be re-applied every 14 days.
Curative fungicide applications for brown patch may not be effective during periods of hot weather because tall fescue does not grow well during these conditions and will recover from brown patch injury very slowly. For this reason, a preventive fungicide program should be considered on tall fescue when conditions are favorable for disease development.