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 Introduction
 Disease management
 Homeowner control options
 Table 1






Title: Pythium blight on overseeded turfgrass
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Permanent Link: http://ufdc.ufl.edu/UF00066808/00001
 Material Information
Title: Pythium blight on overseeded turfgrass
Alternate Title: EDIS PP 203
Physical Description: Book
Language: English
Creator: Harmon, Philip F
Stiles, Carol
Datnoff, L. E ( Lawrence E )
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, EDIS
Place of Publication: Gainesville Fla.
Publication Date: [2004]-
 Subjects
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Summary: Pythium blight or cottony blight rapidly kills cool-season turfgrasses overseeded as winter cover of warm-season species. The disease can occur on bermudagrass in the summer, but disease severity on this warm-season species often is limited when compared to the damage caused to cool-season turfgrass.
System Details: Internet access required.
Statement of Responsibility: Philip F. Harmon, Carol M. Stiles, and Lawrence E. Datnoff.
General Note: Title from Web page viewed on October 22, 2004.
General Note: At head of title: University of Florida, Cooperative Extension Service, Institute of Food and Agricultural Sciences, EDIS.
General Note: "This document is PP 203, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date September 2004."--Footnote.
 Record Information
Bibliographic ID: UF00066808
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 003105333
oclc - 56803367

Table of Contents
    Introduction
        Page 1
    Disease management
        Page 2
    Homeowner control options
        Page 3
    Table 1
        Page 4
Full Text





UNIVERSITY OF

FLORIDA


IFAS EXTENSION


Pythium Blight on Overseeded Turfgrass


Philip F. Harmon, Carol M. Stiles, and Lawrence E. Datnoff2


Pythium blight or cottony blight rapidly kills
cool-season turfgrasses overseeded as winter cover of
warm-season species. The disease can occur on
bermudagrass in the summer, but disease severity on
this warm-season species often is limited when
compared to the damage caused to cool-season
turfgrass. Pythium aphanidermatum as well as other
species, such as P. torulosum, have been associated
with Pythium blight of overseeded turfgrasses in
Florida.

Disease Symptoms and Occurrence

Weather significantly influences disease
outbreaks and severity. Colonization of turf by
Pythium is favored by wet periods and high
temperatures. The pathogen can kill seedlings as well
as an established turfgrass. Temperatures around
900F are ideal for disease development. The
pathogen causes little damage below 680F. In
addition to high temperatures, extended periods of
wet, foggy, or rainy conditions with high humidity
are required for disease development. Frequent
irrigation needed to establish an overseed can favor
disease development during periods of high
temperatures. Symptoms are often first observed in


low areas where surface water runs, pools, and
drains. Severe disease outbreaks commonly occur on
turfgrass sites that are over-irrigated or poorly
drained.

Pythium blight can quickly spread to kill large
areas of turfgrass. When conditions have been
favorable for disease spread, distinct and
well-defined areas of turfgrass may first appear
watersoaked, dark, and wilted (Figure 1). As disease
progresses, the turf will collapse and appear brown
and matted, sometimes with a bronze or red tinge to
the border of the affected area (Figure 2). Extended
periods of high humidity or leaf wetness may result
in a white cottony growth of aerial mycelium on
symptomatic turf (Figure 3). Initial symptoms can
appear to have spread along paths of mechanical
movement of diseased tissue, such as mowing
patterns, and along paths of surface water drainage.
Turfgrass is killed in a radial pattern outward from
the initial disease outbreak as long as conditions are
favorable for disease spread and no fungicide is
applied.

Submission of a sample to a diagnostic clinic to
confirm Pythium blight is recommended, if the turf


1. This document is PP 203, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural
Sciences, University of Florida. Original publication date September 2004. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. Philip F. Harmon and Carol M. Stiles, assistant professor, Lawrence E. Datnoff, professor, Plant Pathology Department, Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the
products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition.
All chemicals should be used in accordance with directions on the manufacturer's label.


PP203


1


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity Affirmative Action Employer authorized to provide
research, educational information and other services only to individuals and institutions that function without regard to race, creed, color, religion,
age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For information on obtaining other extension
publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural
Sciences / University of Florida / Larry R. Arrington, Interim Dean







Pythium Blight on Overseeded Turfgrass 2


M. r
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Figure 1. The initial symptoms of Pythium blight on a
ryegrass overseed of a bermudagrass athletic field. The
first symptoms often include turfgrass with a wilted, greasy,
or gray appearance. Credits: Gail Wisler and Carol Stiles


Figure 2. Pythium blight can rapidly progress into
well-defined areas of blighted and matted turfgrass given
favorable environmental conditions. Credits: Gail Wisler
and Carol Stiles

manager or homeowner is not familiar with this
disease; accurate diagnosis can help reduce the


amount of fungicide use and prevent the use of
fungicides that are not effective against the particular
disease. Disease diagnosis is available for a minimal
fee from the Florida Extension Plant Disease Clinic.


Figure 3. White, airy, cottony growth of the Pythium
pathogen on the expanding edge of a diseased area of
overseed was observed after an extended period of high
relative humidity. Credits: Lawrence Datnoff

Disease Management

All cool-season species commonly used to
overseed turfgrass in Florida are susceptible to
Pythium blight. Though bermudagrass cultivars likely
differ in susceptibility, no significant differences have
been identified. Horticultural practices can influence
Pythium blight, but even ideal practices will not
prevent disease occurrence in all cases, particularly if
environmental conditions become highly favorable.

Irrigation practices should be employed that do
not extend periods of leaf wetness and that do not
waterlog soils, especially in low areas. Improving air
circulation around problematic turfgrass areas by
trimming surrounding foliage or using fans on golf
course greens may help hasten drying of the area and
lessen the likelihood of disease outbreak. Excessive
applications of available nitrogen should be avoided
during and directly prior to disease-favorable
conditions because new lush turfgrass growth seems
to be more susceptible to disease damage. The
disease can be spread by mechanical transmission of
the pathogen, so traffic across affected areas,
including mowing, should be minimized during
periods of pathogen activity.


Pythium Blight on Overseeded Turfgrass


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Pythium Blight on Overseeded Turfgrass 3


Prompt and accurate diagnosis of Pythium blight
is of utmost importance if fungicide applications are
to effectively control disease spread. Products that
control Pythium diseases (Table 1) may not be
effective against other common diseases and vice
versa. Once symptoms are visible, recovery of
affected turfgrass is not possible, and the area may
have to be re-seeded. Applications of the most
effective fungicide products can protect healthy turf,
thereby slowing or stopping disease spread from an
affected area.

When temperatures hover above 800F during
extended moist periods such as frequent irrigation
associated with overseed establishment, Pythium
outbreaks are likely and preventative fungicide
applications are warranted. When applied prior to
seeding, fungicides provide relatively poor control.
However, an application at the time of seeding,
seedling emergence, and one additional application
14 days later generally provide acceptable disease
control when establishing an overseed. After
establishment, preventative applications often are
applied only to problematic areas but sometimes to
entire high-value turfgrass plantings such as athletic
fields and golf course greens, tees, and fairways.
Continued applications according to label directions
may be needed as long as disease-favorable
conditions persist. Populations of Pythium resistant
to some of the fungicides listed in Table 1 have been
reported in some areas. Products with different active
ingredients should be rotated in a spray schedule to
lessen the likelihood of fungicide-resistant
populations developing. Product labels should be
consulted for spray intervals and resistance
management information.

Homeowner Control Options

Good horticultural practices outlined above can
reduce the likelihood of Pythium blight on
overseeded home lawns. If the disease becomes a
persistent problem that requires further attention, it is
recommended that the homeowner seek the services
of a professional lawn care company, since some of
the fungicides listed in Table 1 cannot be applied
without an applicator license or are not labeled for
use in residential lawns. Some homeowners may have
the equipment and knowledge required to correctly


make a fungicide application, including all safety
equipment. If such homeowners understand the risks
to both themselves and the environment, fungicide
products are available through garden centers and
internet catalogs. Some of the fungicides listed in
Table 1 are marketed to homeowners. For example,
Monterey Aliette contains the fungicide aluminum
tris and is available through Monterey Lawn and
Garden Products
(http://www.montereylawngarden.com). Because the
homeowner pesticide market and product availability
can change, consult your local county extension agent
or university specialist for up-to-date product
recommendations.

Any person who applies pesticides should always
read, understand, and follow all label instructions
prior to use. Specific products are listed for example
only. Neither inclusion of products nor omission of
similar alternative products in this publication is
meant to imply any endorsement or criticism.

Related Resources

Managing Pythium Blight in Overseeded Turf.
http://edis.ifas.ufl.edu/PP 115

University of Florida Extension Plant Disease
Clinic.
http://plantpath.ifas.ufl.edu/pdc/Default.htm

University of Florida Pest Control Guide for
Turfgrass Managers, updated yearly.
http://turf.ufl.edu

Turfgrass Disease Management.
http://edis.ifas.ufl.edu/LH040

Florida Cooperative Extension's Electronic Data
Information Source (EDIS)
http://edis.ifas.ufl.edu/

Collecting and Submitting Turf Samples for
Disease Diagnosis http://edis.ifas.ufl.edu/LH041


Pythium Blight on Overseeded Turfgrass


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Pythium Blight on Overseeded Turfgrass 4


Table 1. Fungicides for control of Pythium blight.


Fungicide Product Activity Relative efficacy 1
active ingredient
Preventative 2 Curative 2


aluminum tris Signature systemic *****
mefenoxam 3 Subdue Maxx local systemic *****
azoxystrobin3 Heritage local systemic ** ***
propamocarb Banol local systemic ** *
etridiazole Terrazole contact *
chloroneb Terraneb contact *
mancozeb Fore contact *
*** provides greatest efficacy under disease-favorable conditions
** good management tool under moderate to low disease pressure
* provides some control, best used in rotation or tank mix with other chemistries
2 Preventative- applied before symptoms; Curative- applied after symptoms apparent
3 Risk of resistance in pathogen populations is high. Resistance management, including fungicide rotation, is
required for these fungicides.


Pythium Blight on Overseeded Turfgrass


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