L.P. Tredway, Extension Plant Pathology
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. The most common diseases of tall fescue can be diagnosed by using the descriptions given in this publication. Other diseases, cultural problems, or environmental problems may also occur. There are many resources available to turfgrass managers who require assistance in diagnosing diseases and other problems. The Plant Disease and Insect Clinic at NC State University ( http://www.ces.ncsu.edu/depts/ent/clinic/) specializes in diagnosing turfgrass diseases and other problems. Visit the clinic website for sample submission forms and instructions on collecting and packaging of samples. Consult your local Agricultural Extension agent or University Extension Specialist for additional assistance. Soil samples should be taken regularly to identify nutritional and nematode problems. Fungicide recommendations and other information is available in other publications available through the NC State TurfFiles website (www.turffiles.ncsu.edu).
Diseases and Their Management
Brown PatchBrown 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 (www.turffiles.ncsu.edu) or the National Turfgrass Evaluation Program (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.
Pythium BlightPythium blight is not as common as brown patch, but this disease has the potential to cause a large amount of damage in a short period of time. Pythium blight initially appears as small, sunken circular patches up to 1 foot in diameter during hot, humid weather (Figure 4). Leaves within the patches are matted, orange or dark gray in color, and greasy in appearance. Gray, cottony mycelium may be seen in the infected areas when the leaves are wet or humidity is high (Figure 5). The disease spreads rapidly along drainage patterns and can be tracked by equipment. Pythium blight can cause severe damage quickly because of its rapid spread when conditions are favorable for development.
Pythium blight may develop when night temperatures exceed 65°F in combination with 12 to 14 hours of continuous leaf wetness. Daytime temperatures above 85°F also encourage Pythium blight development, possibly due to increased stress on the turf. Severe Pythium blight epidemics are commonly observed on the morning after a 'pop-up' thunderstorm in the summer months. This disease is encouraged by many of the same factors that encourage brown patch - extended periods of leaf wetness, excessive nitrogen, and wet, compacted soils. Therefore, cultural practices for management of brown patch will also help to minimize Pythium blight development. In addition, do not mow or irrigate when Pythium mycelium is present on the foliage to minimize spread of the pathogen. Collect and promptly dispose of clippings from infected areas and ensure that mowing equipment is washed before going to a non-infected area.Due to the potential for rapid development of Pythium blight, high-value landscapes and athletic fields should be protected with a preventive fungicide program when favorable weather is forecasted. Products containing the active ingredients mefanoxam (Subdue Maxx, Mefanoxam), propamocarb (Banol), or fosetyl-Al (Signature) will provide up to 21 days of preventative Pythium blight control. If Pythium blight symptoms are observed, mefanoxam and propamocarb are more effective than fosetyl-Al for curative control. Addition of a contact fungicide, such as mancozeb (Fore, Dithane, Mancozeb, others), can help improve curative control because of their fast-acting fungicidal effects.
Gray Leaf Spot Gray leaf spot was first documented as a disease of tall fescue in the mid-1990's, and is now a consistent problem throughout the Southeastern United States. Recently developed tall fescue cultivars with increased brown patch resistance tend to be more susceptible to gray leaf spot, which may explain the recent appearance of the disease. Gray leaf spot is most damaging in newly established turfgrass stands. The disease is typically most severe in the first year of establishment, but then gradually becomes less of a problem as the turf stand matures
Gray leaf spot initially appears as spots on the leaves that are round or oval, tan in color, and with a dark brown border (Figure 6). When the leaves are wet or humidity is high, the leaf spots turn gray and fuzzy with profuse spore production (Figure 7). This "leaf spot phase" of the disease does not typically cause significant damage to the turf stand. However, the leaf spots eventually expand and girdle the leaf, marking the beginning of the "foliar blight phase" of the disease, which causes significant damage to the turf stand. Foliar blighting initially occurs in patches from 6 to 12 inches in diameter that are orange to yellow in color (Figure 8). The leaves within the blighted patches are typically matted and greasy in appearance, and may appear similar to patches caused by Pythium blight. These patches can rapidly coalesce to produce large, irregular areas of damaged turf.
Most cases of gray leaf spot occur from late July through September. Gray leaf spot may develop when temperatures are between 70°F and 95°F, but the fungus also requires at least 14 hours of continuous leaf wetness in order to initiate infection. Gray leaf spot develops to some extent in most years, but severe foliar blighting only occurs every 3 to 5 years when several consecutive days of warm, wet, overcast weather occur in late summer. Any factor that increases the amount of leaf wetness will increase gray leaf spot development. Lush leaf tissue produced by turf that is fertilized with excessive nitrogen is far more prone to infection by gray leaf spot.
As indicated above, cultivars of tall fescue vary widely in gray leaf spot susceptibility. The cultivars that are most resistant to gray leaf spot, however, are highly susceptible to brown patch. Blending of brown patch-resistant varieties with gray leaf spot -resistant varieties may be effective for minimizing both of these diseases. However, since brown patch is a more consistent and severe problem in tall fescue, the majority of the blend should be comprised of varieties with resistance to brown patch.
Stress of any kind will encourage gray leaf spot development in tall fescue. If possible, control traffic on tall fescue athletic fields by limiting access or rotating fields when gray leaf spot is developing. Proper mowing, fertilization, and irrigation practices will reduce the chances of significant turf loss from this disease. Do not apply nitrogen to tall fescue in late spring or summer. Irrigate deep and infrequent, applying sufficient water to wet the entire root zone and repeating only when the entire root zone is not longer moist. Schedule irrigation early in the morning, before sunrise, and never in the late afternoon, evening, or before sunrise. Mowing should be conducted at 2.5 to 3 inches, using the "1/3 rule" as a guide for mowing frequency. Collect and dispose of leaf clippings when gray leaf spot is active to reduce further spread of the disease.
Fungicides containing the active ingredients azoxystrobin (Heritage), pyraclostrobin (Insignia), trifloxystrobin (Compass), and thiophanate-methyl (Cleary 3336, Systar) are most effective for gray leaf spot control. These fungicides are best when applied on a preventative or early curative basis, but must be applied before the foliar blight stage appears for best results. Fungicide resistance develops rapidly in populations of the gray leaf spot pathogen, so it is important to rotate among different classes of fungicides to delay the development of resistance. Tank-mixing these systemic fungicides with the contacts fungicides chlorothalonil (Daconil, Chlorstar, Manicure) or mancozeb (Fore, Dithane, Mancozeb) will also help to prevent fungicide resistance. Repeat treatments may be necessary if conditions favoring the disease persist. Flutolanil (ProStar) and iprodione (Chipco 26GT) have no activity against gray leaf spot.
Immature stands of tall fescue are far more prone to brown patch, Pythium blight, and gray leaf spot than mature stands. When establishing a new stand of tall fescue, use recommended seeding rates to allow rapid maturation of new seedlings. The use of high seeding rates, above 5 lbs per 1000 ft2, produces a dense stand of seedlings that retains moisture and humidity for extended periods of time and encourages the development of foliar diseases. Also when seeding rates are high, competition among seedlings slows their maturation rate and extends their window of susceptibility to these diseases.
Net BlotchNet blotch is a Helminthosporium disease that occurs on tall fescue, but this disease normally does not cause severe damage. The symptoms of net blotch are dark brown "net" patterns on the leaves (Figure 9). Net blotch is commonly seen during extended periods of cool, cloudy, wet weather that stunts the growth of tall fescue. The disease can cause significant damage to tall fescue when these conditions are combined with turf that has been fertilized with excessive nitrogen. Fertilize to meet the nutritional needs of the turf, but avoid over-stimulation and the development of lush, succulent growth.
In general, tall should not receive more than one pound of nitrogen per 1,000 square feet in a single application, and at least 50% of the nitrogen should be in a slow release form. Low mowing heights tend to increase the severity of net blotch, so tall fescue should be mowed at 2.5 to 3 inches to minimize development of this disease. Collecting and disposing of leaf clippings when the disease is active may also help to slow spread of the disease. Reduce extended periods of leaf wetness by watering deeply but infrequently to wet the entire root zone. Do not irrigate just before or after sunrise and ensure good surface and soil drainage. Fungicides are available for control of net blotch, but should not be needed if the above steps are taken to manage the disease culturally.RustRust occurs on tall fescue and is seen most often during periods of cool, cloudy weather in spring, late summer, or fall. Early symptoms include small, yellow flecks that develop on the leaves and stems (Figure 10). The flecks expand over time into yellow, raised pustules that eventually rupture to release powdery masses of yellow spores (Figure 11). Heavily infected areas become thin and will exhibit clouds of yellow spores when the foliage is disturbed (Figure 12). The rust pustules on infected leaves turn black in color during the fall as temperatures cool (Figure 13).
Rust is most severe in tall fescue that is growing slowly due to adverse weather conditions or inadequate management. Low light intensity, inadequate fertilization, drought stress, and infrequent mowing favor greatly encourage rust development. Maintaining a balanced fertility program and preventing drought stress will reduce rust severity.
Submit a soil sample for nutrient analysis at least once per year, and apply the recommended amounts of phosphorus, potassium, and lime. Nitrogen should be applied as needed in the spring and fall to maintain vigorous vegetative growth. Extended periods of leaf wetness are also required for rust to develop, so deep and infrequent irrigation is important for management of this disease. Mow the turf on a regular basis, removing no more than 30 to 40 percent of the foliage in one mowing. Collect and dispose of clippings taken from infected areas to avoid spread of this disease and wash off equipment before entering non-infected areas. Several fungicides can be used to control rust diseases, but are usually not necessary if the above steps are taken to manage the disease culturally.**April 2005