Red Leaf Spot
[Drechslera
erythrospila]
SYMPTOMS
Red leaf
spot is a disease that occurs on creeping bentgrass during warm and wet weather
in the spring, summer, or fall. Red leaf spot is a ‘Helminthosporium’ disease,
which is a complex of diseases caused by fungi that produce large, cigar-shaped
spores. Symptoms of red leaf spot appear in spots or irregular patches that are
red or reddish-brown. On individual plants, symptoms appear as small, red or
reddish-brown leaf spots with a tan center. As the lesions expand and coalesce,
the turfgrass leaves become blighted and collapse to the ground.
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red leaf spot plant symptoms
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Characteristic
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Description
|
|
Host
Grass Species
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creeping
bentgrass
|
|
Month(s)
with symptoms
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April
to October
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|
Stand
Symptoms
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spots,
patches (4 to 12 inches)
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|
Foliar
Symptoms - Location/Shape
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oval
leaf spots
|
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Foliar
Symptoms - Color
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small,
red or reddish-brown leaf spots with a tan center
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Root/Crown
Symptoms
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none
|
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Fungal
Signs
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none
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Note: Still not
sure if this is the right disease? The Turfgrass Disease
Identification program may be helpful. Or consult the experts at the Turf
Diagnostics Lab. Check the TurfFiles glossary for definitions
of unfamiliar terms.
FACTORS
AFFECTING DISEASE DEVELOPMENT
Red leaf spot is one of several
Helminthosporium diseases which survive in thatch during periods that are
unfavorable for disease development. The red leaf spot pathogen is most active
during warm, wet weather in the late spring, summer, or early fall.
Red leaf spot is most severe on
turf that is growing slowly due to adverse weather conditions or improper
management practices. Shaded areas with little or no air movement result in
weak turf and extended periods of leaf wetness that favor disease development
and plant infection. Deficient or excessive nitrogen, excessive thatch,
extended periods of leaf wetness, drought stress, and low mowing heights are
factors that encourage the development of Helminthosporium diseases.
Certain cultivars of turfgrasses
are very susceptible to injury from Helminthosporium diseases while many of the
newly released cultivars have exhibited good resistance.
CULTURAL
CONTROL
Use turfgrass cultivars with
resistance to this disease when available. Use of resistant cultivars is one of
the best means of prevention. Select cultivars based on regional trials and
University recommendations. Use blends and mixtures of cool-season grasses
whenever possible.
Fertilize to meet the nutritional
needs of the turf but avoid over-stimulation and the development of lush,
succulent growth. Do not apply more than one pound of nitrogen per 1000 ft2
in a single application. Creeping bentgrass should be mowed at heights between
0.1” and 0.125” during fall, winter, and spring and between 0.125” and 0.15”
during summer. Keep the mower blades sharp to prevent open wounds through which
the fungus can enter.
Reduce extended periods of leaf
wetness with deep and infrequent irrigation, wetting the entire root zone then
re-applying when the root zone becomes dry. Do not irrigate just before or
after sunrise and remove dew in the morning to shorten leaf wetness periods.
Remove unwanted vegetation that impedes air movement and prune trees to
increase light penetration. Regular aerification and topdressing is needed to
reduce thatch accumulations and minimize pathogen survival.
CHEMICAL
CONTROL
Red leaf spot can be controlled
on a preventative or curative basis. Where the disease has been a persistent
problem, apply an effective fungicide every 14 to 21 days when conditions are
favorable for infection. Once the symptoms of read leaf spot appear, tank-mixtures
of contact and systemic fungicides are recommended for curative control.
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Fungicide
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Efficacy (1)
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Resistance Risk (2)
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Class (3)
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Products (4)
|
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iprodione**
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++++
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4
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dicarboxamide
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26GT, Iprodione Pro
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vinclozolin**
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++++
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4
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dicarboxamide
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Curalan, Touche
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iprodione + thiophanate-methyl**
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++++
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6
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dicarboxamide + benzimidazole
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26/36, Fluid Fungicide, Pro Turf
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mancozeb**
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++++
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2
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dithiocarbamate
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Fore, Dithane, Pentathlon, Protect
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mancozeb + copper hydroxide**
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++++
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2
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dithiocarbamate
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Junction
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azoxystrobin
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++++
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6
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QoI
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Heritage
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azoxystrobin + propiconazole
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++++
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6
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QoI + DMI
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Headway
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chlorothalonil**
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+++
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2
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nitrile
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Daconil, Chlorostar, Echo, Manicure
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chlorothalonil + thiophanate-methyl**
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+++
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4
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nitrile + benzimidazole
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Spectro, ConSyst
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chlorothalonil + propiconazole**
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+++
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3
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nitrile + DMI
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Concert
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chlorothalonil + propiconazole + fludioxonil**
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+++
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3
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nitrile + DMI + phenylpyrolle
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Instrata
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pyraclostrobin
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+++
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6
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QoI
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Insignia
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propiconazole
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++
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4
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DMI
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Banner MAXX, Propiconazole G-Pro, Propiconazole Pro,
Quali-Pro Propiconazole, Savvi, Spectator
|
|
myclobutanil
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+
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4
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DMI
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Eagle
|
|
thiophanate-methyl
|
?
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6
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benzimidazole
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3336, Fungo, T-Storm
|
|
flutolanil + thiophanate-methyl
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?
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6
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carboxamide + benzimidazole
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SysStar
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triticonazole
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?
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2
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DMI
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Trinity, Triton
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triadimefon + trifloxystrobin
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?
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6
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DMI + QoI
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Tartan, Armada
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fludioxonil
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?
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2
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phenylpyrolle
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Medallion
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fluoxastrobin
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?
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6
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QoI
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Disarm
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trifloxystrobin
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?
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6
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QoI
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Compass
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** Not for application to residential
lawns.
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Footnotes:
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(1)
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Efficacy Codes:
|
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++++
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excellent control when
conditions are highly favorable for disease development
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+++
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good control when disease pressure
is high, or excellent control when disease pressure is moderate
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|
++
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good control when disease
pressure is moderate, excellent control when disease pressure is low
|
|
+
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good control when disease
pressure is low
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0
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does not
provide adequate control under any conditions
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|
?
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cannot be rated due to
insufficient data
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(2)
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Resistance Risk:
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1
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Rotating and tank-mixing not
necessary, but recommended to avoid potential side effects from continuous use
of same chemical class.
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|
2
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Rotate to different chemical
class after 3-4 applications; tank-mixing not necessary.
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3
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Rotate to different chemical
class after 2-3 applications; tank-mixing not necessary.
|
|
4
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Rotate to different chemical
class after 1-2 applications; tank-mixing not necessary.
|
|
6
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Rotate to different chemical
class after 1-2 applications; tank-mixing with low or moderate risk product
recommended.
|
|
9
|
Rotate to different chemical class
after EVERY application; tank-mix with low or moderate risk product for EVERY
application.
|
|
(3)
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Continual use of fungicides
with similar control mechanisms (modes of action) can result in fungi that
are resistant to some chemicals. Poor or ineffective disease control can be
expected when this occurs. Managers can reduce the chances of this happening
by mixing or alternating fungicides belonging to different chemical classes.
|
|
(4)
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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 may vary widely, performance of the chemical will not always
conform to the safety and pest control standards indicated by experimental
data. When more than one brand name exists for an agricultural chemical, the
name of brand that first came onto the market is listed first. Otherwise,
brand names are listed in alphabetical order. The order in which brand names
are given is not an indication of a recommendation or criticism.
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Recommendations for the use of
agricultural chemicals are included in this publication as a convenience to
the reader. The use of brand names and any mention or listing of commercial
products or services does not imply endorsement by North Carolina State University or discrimination against similar products or services not mentioned. Other
brand names may be labeled for use on turfgrasses. Individuals who use agricultural
chemicals are responsible for ensuring that the intended use complies with
current regulations and conforms to the product label. Be sure to obtain
current information about usage regulations and examine a current product
label before applying any chemical. For assistance, contact your county's
Cooperative Extension agent.
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© North Carolina
State University. This information sheet was prepared by Lane P. Tredway, Gail
G. Wilkerson, Bridget R. Lassiter, Jenifer J. Reynolds, and Gregory S. Buol.
Departments of Plant Pathology and Crop Science, College of Agriculture &
Life Sciences, North Carolina State University. Prepared March
23, 2009. Available on-line at www.turffiles.ncsu.edu. This publication was
made possible through a grant provided by the Center for Turfgrass
Environmental Research & Education (CENTERE) whose purpose is to support
worthwhile projects that will benefit both the private sector and the public,
and protect the environment.