Pythium Blight
[Pythium
aphanidermatum]
SYMPTOMS
Pythium
blight first appears as small, sunken, circular patches up to 1 foot in
diameter during hot, humid weather. 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.
The disease spreads rapidly along drainage patterns and can be tracked by
equipment. This disease can spread rapidly and cause severe damage to a turf
stand very quickly when conditions are favorable for development.
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Pythium blight mycellium in tall fescue
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Characteristic
|
Description
|
|
Host
Grass Species
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bentgrass,
bluegrasses, fescues, ryegrasses
|
|
Month(s)
with symptoms
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June to
August
|
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Stand
Symptoms
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patches
(4 to 12 inches), irregular distribution across turf stand
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|
Foliar
Symptoms - Location/Shape
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blighting
of entire leaves
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Foliar
Symptoms - Color
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tan,
brown, black, gray, orange
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|
Root/Crown
Symptoms
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none
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Fungal
Signs
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mycelium
or 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
Pythium blight may develop
when night temperatures exceed 65°F and leaves are continually wet for 12 to 14
hours for several consecutive nights. 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 the
morning after a late afternoon or early evening thunderstorm in the summer.
Excessive soil moisture and succulent foliar growth also favor disease
development.
Perennial ryegrass and annual
bluegrass are most prone to Pythium blight and can sustain significant
damage in 2 to 3 days when conditions are favorable. Creeping bentgrass and
tall fescue are more resistant to the disease, but can be severely affected if
conditions are conducive for prolonged periods.
CULTURAL
CONTROL
Reduce prolonged leaf wetness by
watering before sunrise and on a deep and infrequent basis. Avoid excessive
rates of nitrogen to prevent lush, succulent foliar growth, which is very
susceptible to Pythium blight. Cool-season turfgrasses should not be
fertilized with more than 0.25 lb N per 1000 ft2 when conditions
favor Pythium blight activity. Avoid establishing turf in low-lying
areas that will collect water. If necessary, install subsurface drainage to
prevent wet soil conditions. Relieve compaction and maintain soil drainage
through hollow tine aerification, and topdress golf course putting greens
regularly to minimize thatch accumulations.
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 an uninfected area.
CHEMICAL
CONTROL
Due to the potential for rapid
development of this disease, high value areas and susceptible grasses should be
protected with a preventive fungicide program. Applications should be initiated
when night temperatures consistently exceed 65°F and repeated on 14 to 21 day
intervals as directed on the fungicide label.
|
Fungicide
|
Efficacy (1)
|
Resistance Risk (2)
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Class (3)
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Products (4)
|
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propamocarb
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++++
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3
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carbamate
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Banol
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propamocarb + fluopicolide**
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++++
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6
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carbamate
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Stellar
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mefenoxam
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++++
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9
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phenylamide
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Subdue, Fenox, Mefenoxam, Quell
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fosetyl-Al**
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++++
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3
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phosphonate
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Signature
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cyazofamid
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++++
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9
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QiI
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Segway
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phosphorous acid
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+++
|
3
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phosphonate
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Alude, Magellan, Vital, Resyst
|
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mancozeb**
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++
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3
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dithiocarbamate
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Fore, Dithane, Protect
|
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mancozeb + copper hydroxide**
|
++
|
3
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dithiocarbamate
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Junction
|
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pyraclostrobin
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++
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9
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QoI
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Insignia
|
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chloroneb
|
+
|
3
|
aromatic hydrocarbon
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Teremec, Terraneb
|
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ethazole**
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+
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3
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aromatic hydrocarbon
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Koban, Terrazole
|
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maneb**
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+
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3
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dithiocarbamate
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Pentathlon
|
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azoxystrobin
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+
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9
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QoI
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Heritage
|
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fluoxastrobin
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+
|
9
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QoI
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Disarm
|
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azoxystrobin + propiconazole
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+
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9
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QoI + DMI
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Headway
|
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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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excellent control when
conditions are highly favorable for disease development
|
|
+++
|
good control when disease
pressure is high, or excellent control when disease pressure is moderate
|
|
++
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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
|
|
?
|
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.
|
|
2
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Rotate to different chemical class
after 3-4 applications; tank-mixing not necessary.
|
|
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.
|
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6
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Rotate to different chemical
class after 1-2 applications; tank-mixing with low or moderate risk product
recommended.
|
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9
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Rotate to different chemical
class after EVERY application; tank-mix with low or moderate risk product for
EVERY application.
|
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(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)
|
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.
|
|
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 Fred Yelverton, Gail
G. Wilkerson, Leon Warren, Travis Gannon, and Gregory S. Buol. Department of
Crop Science, College of Agriculture & Life Sciences, North Carolina State
University. Prepared November, 3, 2008. 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.