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Turfgrass Disease Information Note 6 (TURF-006)
Lane P. Tredway, Extension Turfgrass Pathologist |
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 Figure 1: Brown patch symptoms from a distance. |
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 (Figure
3).
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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 (www.turffiles.ncsu.edu) or the National Turfgrass Evaluation Program (www.ntep.org). |
 Figure 2: Brown patch lesions on a tall fescue leaf. |
 Figure 3: Brown patch pathogen spreading by mycelium. |
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. |
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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. |
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Pythium 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. |  Figure 4:
Symptoms of Pythium blight on tall fescue. |
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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.
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 Figure 5: Mycelium produced by Pythium blight pathogen. |
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.
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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.
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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. |
 Figure 6:
Gray leaf spot symptoms on tall fescue leaf. |
 Figure 7: Spore production by gray leaf spot pathogen. |
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.
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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.
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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. |
Figure 8:
Foliar blight symptoms caused by gray leaf spot. |
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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.
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 Figure 9:
Leaf spots caused by net blotch on tall fescue. |
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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.
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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.
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 Figure 10:
Early symptoms of rust on tall fescue. |
Rust
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).
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 Figure 11:
Rust pustules rupturing to release spores. |
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. |
Figure 12:
Rust causes yellowing and thinning of turf in irregular patterns. |
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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. |
 Figure 13:
Rust pustules turn black in fall. |
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Diagnosis and Management of Tall Fescue Diseases
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). |
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Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies. Published by the North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating. Last update to information: April 2005 |