Diseases ›

Pythium Root Rot

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.

Development Factors

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 cyazofamid, mefenoxam, 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 cyazofamid, mefenoxam, or propamocarb 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. Other fungicides should also be watered-in to drive the active ingredient into the root zone where the Pythium root rot pathogens are most active.

Fungicide and Formulation1
Amount of Formulation2
Application Interval3
Efficacy Rating
Resistance Risk
Fungicide and Formulation1

azoxystrobin
(Heritage, Strobe)
(Heritage TL)
(Heritage G)
(Strobe L)

Amount of Formulation2


0.4
2
2 to 4
0.38 to 0.77

Application Interval3


10 to 14
10 to 14
10 to 14
10 to 14

Efficacy Rating

++



Resistance Risk

Medium



Fungicide and Formulation1

azoxystrobin + propiconazole (Headway)
ME
G

Amount of Formulation2


3
2 to 4 lbs

Application Interval3


10 to 14
14 to 28

Efficacy Rating

++

Resistance Risk

Medium

Fungicide and Formulation1

azoxystrobin + tebuconazole (Strobe T)*

Amount of Formulation2

0.75 to 1.5

Application Interval3

10 to 21

Efficacy Rating

++

Resistance Risk

Medium

Fungicide and Formulation1

chlorothalonil + fluoxastrobin (Fame C)*

Amount of Formulation2

3 to 5.9

Application Interval3

7 to 10

Efficacy Rating

++

Resistance Risk

Medium

Fungicide and Formulation1

cyazofamid (Segway)*

Amount of Formulation2

0.45 to 0.9

Application Interval3

14 to 21

Efficacy Rating

++++

Resistance Risk

Medium

Fungicide and Formulation1

ethazole
(Koban)*
(Terrazole)*

Amount of Formulation2


4.5
2 to 4

Application Interval3


10
10 to 14

Efficacy Rating

+++

Resistance Risk

Low

Fungicide and Formulation1

fluoxastrobin (Fame)
SC
G

Amount of Formulation2


0.18 to 0.36
2.3 to 4.6 lbs

Application Interval3


7 to 10
14

Efficacy Rating

++

Resistance Risk

Medium

Fungicide and Formulation1

fluoxastrobin + tebuconazole (Fame T)*

Amount of Formulation2

0.45 to 0.9

Application Interval3

21

Efficacy Rating

++

Resistance Risk

Medium

Fungicide and Formulation1

fosetyl Al
(Signature, Fosetyl-AI )
(Signature Xtra Stressgard)*
potassium phosphite (Appear)

Amount of Formulation2


4 to 8
2 to 6
6 to 8

Application Interval3


14 to 21
7 to 21
7 to 14

Efficacy Rating

+++


?

Resistance Risk

Low


?

Fungicide and Formulation1

propamocarb (Banol)*

Amount of Formulation2

1.3 to 4

Application Interval3

7 to 21

Efficacy Rating

++

Resistance Risk

Medium

1 Other trade names with the same active ingredients are labeled for use on turfgrasses and can be used according to label directions.
2 Apply fungicides in 2 to 5 gallons of water per 1,000 square feet according to label directions. Use lower rates for preventive and higher rates for curative applications.
3 Use shorter intervals when conditions are very favorable for disease.
* Products marked with an asterisk are not labeled for home lawn use.

Efficacy Rating
++++ = excellent control when conditions are highly favorable for disease development
+++ = good control when disease pressure is high, 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
? = not rated due to insufficient data

Resistance Risk
Low = Rotate to different chemical class after 3-4 applications; tank mixing not necessary
Medium = Rotate to different chemical class after 1-2 applications; tank-mixing with low or medium risk product recommended
High = Rotate to different chemical class after EVERY application; tank-mix with low or medium risk product for EVERY application
? = not rated due to insufficient data

Presentations

Publications

Species Data

Host species

all

pythium rootrotbent2 ltc
pythium rootrotbent2 ltc
pythium rootrotbent2 ltc
pythium rootrotbent3 ltc
pythium rootrotbent3 ltc
pythium rootrotbent3 ltc
pythium rootrotbent4 ltc
pythium rootrotbent4 ltc
pythium rootrotbent4 ltc
pythium rootrotbent5 ltc
pythium rootrotbent5 ltc
pythium rootrotbent5 ltc
pythium rootrotbent ltc
pythium rootrotbent ltc
pythium rootrotbent ltc
Months with symptoms

all

Stand symptoms

irregular distribution across turf stand

pythium rootrotbent2 ltc
pythium rootrotbent2 ltc
pythium rootrotbent2 ltc
pythium rootrotbent3 ltc
pythium rootrotbent3 ltc
pythium rootrotbent3 ltc
pythium rootrotbent4 ltc
pythium rootrotbent4 ltc
pythium rootrotbent4 ltc
pythium rootrotbent5 ltc
pythium rootrotbent5 ltc
pythium rootrotbent5 ltc
pythium rootrotbent ltc
pythium rootrotbent ltc
pythium rootrotbent ltc
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