Pythium Root Rot
[Pythium
spp.]
SYMPTOMS
Pythium
root rot is a persistent problem in areas that are poorly drained or
over-irrigated. The disease can also occur in well-drained areas following
extended periods of rainfall. Pythium root rot can occur at any time of
the year as long as the soil remains saturated for several days or weeks. From
a distance, symptoms are orange or yellow and usually appear in irregular
patterns, but occasionally develop in spots or distinct patches. Symptoms of Pythium
root rot may spread in drainage patterns during periods of heavy rainfall. On
individual plants, the crowns, roots, rhizomes, and/or stolons will appear dark
and greasy. The depth and density of roots will be drastically reduced in
affected areas.
|
pythium root rot on bentgrass
|
Characteristic
|
Description
|
|
Host
Grass Species
|
all
|
|
Month(s)
with symptoms
|
all
|
|
Stand
Symptoms
|
irregular
distribution across turf stand
|
|
Foliar
Symptoms - Location/Shape
|
dieback
from leaf tip, blighting of entire leaves
|
|
Foliar
Symptoms - Color
|
tan,
yellow, orange
|
|
Root/Crown
Symptoms
|
roots,
stolons, rhizomes, and/or crowns dark brown or black
|
|
Fungal
Signs
|
none
|
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
There are many species of Pythium
that have the ability to cause root rot of turfgrasses. As a result, Pythium
root rot can develop at any time during the growing season if the soil remains
saturated for prolonged periods. Poor surface or subsurface drainage,
over-irrigation, heavy rainfalls, and excessive thatch and organic matter
accumulation are the most common factors that lead to a Pythium root rot
outbreak.
CULTURAL
CONTROL
Avoid establishing turfgrasses in
poorly drained areas that remain saturated for extended periods. Golf course
putting greens must be aerified and topdressed regularly to control thatch and
reduce organic matter accumulation. In general, 15% to 20% of the putting green
surface area should be impacted by hollow-tine aerification annually, and 5000
lbs of topdressing should be applied per 1000 ft2 each year. Pruning
or removal of trees surrounding putting greens to increase sunlight penetration
and air movement will reduce Pythium root rot activity. Installation of
high-powered fans will also help to alleviate the problem where air movement is
restricted. For golf course putting greens with poor internal drainage,
reconstruction is the only practical long-term solution for Pythium root
rot.
CHEMICAL
CONTROL
Little is known about the
relative efficacy of fungicides for Pythium root rot control. Where this
disease has been a persistent problem, apply mefanoxam, fosetyl-Al, or
propamocarb every 14 to 21 days during the growing season or when rainfall
occurs for 2 to 3 consecutive days. For curative applications, first apply
ethazole then follow with an application of mefanoxam 2 to 3 days later. To
minimize the potential for foliar burn, ethazole must be watered-in immediately
after application with at least 1/8” of water. Applications of mefanoxam or
propamocarb should also be watered-in, but fosetyl-Al should be applied to the
foliage for best results.
|
Fungicide
|
Efficacy (1)
|
Resistance Risk (2)
|
Class (3)
|
Products (4)
|
|
ethazole**
|
+++
|
2
|
aromatic hydrocarbon
|
Koban, Terrazole
|
|
mefenoxam
|
++
|
6
|
phenylamide
|
Quell
|
|
fosetyl-Al**
|
?
|
2
|
phosphonate
|
Signature
|
|
azoxystrobin
|
?
|
6
|
QoI
|
Heritage
|
|
fluoxastrobin
|
?
|
6
|
QoI
|
Disarm
|
|
azoxystrobin + propiconazole
|
?
|
6
|
QoI + DMI
|
Headway
|
|
** Not for application to residential
lawns.
|
|
Footnotes:
|
|
(1)
|
Efficacy Codes:
|
|
++++
|
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
|
|
++
|
good control when disease
pressure is moderate, excellent control when disease pressure is low
|
|
+
|
good control when disease
pressure is low
|
|
0
|
does not
provide adequate control under any conditions
|
|
?
|
cannot be rated due to
insufficient data
|
|
(2)
|
Resistance Risk:
|
|
1
|
Rotating and tank-mixing not
necessary, but recommended to avoid potential side effects from continuous use
of same chemical class.
|
|
2
|
Rotate to different chemical
class after 3-4 applications; tank-mixing not necessary.
|
|
3
|
Rotate to different chemical
class after 2-3 applications; tank-mixing not necessary.
|
|
4
|
Rotate to different chemical
class after 1-2 applications; tank-mixing not necessary.
|
|
6
|
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)
|
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.
|
© 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.