NC State Extension Publications

Symptoms

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Red thread develops in circular or irregular patches from 4 inches to 2 feet in diameter. Affected leaves within these patches are tan or bleached-white in color. From a distance, the patches usually have a reddish appearance, due to the presence of thick, red strands of fungal growth emanating from the affected leaves. It is through production of these “red threads (sclerotia)” that the fungus spreads to healthy plants and survives unfavorable conditions. Small tufts of pink, fuzzy mycelium may also be present in or around the patches when the leaves are wet or humidity is high. After prolonged periods of disease development, the patches may merge to produce large irregularly shaped areas of damaged turf.

Development Factors

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The red thread fungus is able to cause disease at temperatures ranging from 40 to 80°F, but develops most rapidly at approximately 70°F. Red thread affects grass that is growing slowly for any reason: inadequate fertilization, drought stress, cool weather, low light intensity, excessive traffic, or many other pest or environmental stresses.

Red thread is most severe in the spring and fall, when extended periods of cool, wet, and overcast weather slow growth of the turf and favor growth of the pathogen. Because of its wide temperature range, red thread can develop at any time of year when a slow-growing host and sufficient leaf wetness are available.

Cultural Control

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Fertilize to meet the nutritional needs of the turf and maintain vigorous growth. Submit a soil sample for nutrient analysis regularly, and apply recommended amounts of phosphorus, potassium, and lime. Apply nitrogen based on university recommendations to prevent weak, thin turf; however, avoid overstimulation and the development of lush, succulent turf.

Irrigation should be performed between midnight and 6 AM to prevent prolonged periods of leaf wetness. Never irrigate in the late afternoon or early evening. Apply a sufficient amount of water to wet the entire root zone, then reapply when the turf first starts to show signs of drought stress. Prune or remove trees, shrubs, or other barriers to increase air movement and sunlight penetration. Remove clippings from affected areas when the disease is active to reduce spread of the disease, and wash infected clippings from equipment before entering uninfected areas.

Chemical Control

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Fungicides are available for control of red thread, but are usually not necessary if proper cultural practices are implemented.

Fungicide and Formulation1FRA Amount of Formulation2 Application Interval (Days)3 Efficacy Rating Resistance Risk FRAC Code4
azoxystrobin
(Heritage, Strobe)
(HeritageTL)
(Heritage G)
(Strobe L)

0.2 to 0.4
1 to 2
2 to 4 lbs
0.38 to 0.77

14 to 28
14 to 28
14 to 28
14 to 28
++++ Low 11
azoxystrobin + acibenzolar-S-methyl (Heritage Action)* 0.2 to 0.4 14 to 28 ++++ Low 11/P01
azoxystrobin + chlorothalonil (Renown)* 2.5 to 4.5 14 to 21 ++++ Low 11/M5
azoxystrobin + difenoconazole (Briskway)* 0.5 to 1.2 14 to 28 ++++ Low 11/3
azoxystrobin + propiconazole (Headway)
ME
G

1.5 to 3
2 to 4 lbs

14 to 28
14 to 28
++++ Low 11/3
azoxystrobin + tebuconazole (Strobe T)* 0.75 to 1.5 14 to 21 ++++ Low 11/3

benzovindiflupyr + difenoconazole (Ascernity)*

1.0 14 ++++ Low 7/3
chlorothalonil
(Daconil Ultrex)*

(Daconil Weather Stik, Legend)*

(Daconil Zn)*

(Chlorothalonil 500ZN)*

(Chlorothalonil 720SFT)*

(Chlorothalonil)*

1.8 to 3.25
3.25 to 5
2 to 5.5
5.5
3 to 5
5.3 to 8
3 to 5
7.9
2.12 to 3.5
5.5
1.8 to 3.2

7 to 10
14
7 to 14
14
7 to 10
14
7 to 10
14
7 to 10
14
7 to 10
+++ Low M5
chlorothalonil + acibenzolar-S-methyl (Daconil Action)* 2 to 3.5
3.6 to 5.4
7 to 10
14
+++ Low M5/P01
chlorothalonil + fluoxastrobin (Fame C)* 3 to 5.9 14 to 28 ++++ Low M5/11
chlorothalonil + iprodione + thiophanate-methyl + tebuconazole (Enclave)* 3 to 4
7 to 8
14 to 21
28
+++ Low M5/2/1/3
chlorothalonil + propiconazole (Concert)* 3 to 5.5
5.5 to 8.5
7 to 14
14 to 21
+++ Low M5/3
chlorothalonil + propiconazole + fludioxonil (Instrata)* 2.75 to 6 14 to 21 +++ Low M5/3/12
chlorothalonil + thiophanate-methyl
(Spectro)*
(TM/C)

3.72 to 5.76
3 to 8

14
14 to 21
+++ Low M5/1

cyazofamid + azoxystrobin (Union)

2.9 to 5.75 14 to 28 ++++ Low 21/11
fluoxastrobin (Fame) 0.18 to 0.36 14 to 28 ++++ Low 11
fluoxastrobin + tebuconazole (Fame T)* 0.45 to 0.9 21 to 28 ++++ Low 11/3
flutolanil
(Prostar)
(Pedigree)

1.5
2.2

21 to 28
21 to 28

++++
++++
Low 7
iprodione (26GT, Iprodione Pro, IPro)* 4 14 ++++ Low 2
iprodione + thiophanate-methyl (26/36)* 2 to 4 14 to 21 ++++ Low 2/1
iprodione + trifloxystrobin (Interface)* 3 to 4 14 +++ Low 2/11
myclobutanil (Eagle, Myclobutanil) 1.2 14 to 21 ++ Low 3
penthiopyrad (Velista) 0.3 to 0.5 14 ? ? 7
polyoxin D
(Affirm)
(Endorse)
0.88
4
7 to 14
7 to 14
? Low 19
propiconazole (Banner MAXX, Propiconazole) 2 14 to 21 +++ Low 3

pydiflumetofen + azoxystrobin + propiconazole (Posterity XT)*

1.5 to 3 14 to 28 ++++ Low 7/11/3
pyraclostrobin (Insignia)
WG
SC

0.5 to 0.9
0.4 to 0.7

14 to 28
14 to 28
++++ Low 11
pyraclostrobin + boscalid (Honor)* 0.55 to 1.1 14 to 28 ++++ Low 11/7
pyraclostrobin + fluxapyroxad (Lexicon Intrinsic) 0.34 to 0.47 14 ++++ Low 11/7
thiophanate-methyl
(3336)
(3336 Plus)
(TM WDG)
(3336 G)
(TM L)

2 to 4
2 to 4
0.67 to 1.3
1.5 to 6 lbs
1 to 2

14
14 to 28
14
14
14
+ Low 1
triadimefon (Bayleton) 0.5 to 1 15 to 30 ++ Low 3
trifloxystrobin (Compass) 0.1 to 0.15
0.2 to 0.25
14
21
++ Low 11
trifloxystrobin + triadimefon
(Armada)
(Tartan)*

0.6 to 1.2
1 to 2

14 to 28
14 to 28
+++ Low 11/3
triticonazole
(Trinity)
(Triton)

0.5 to 1
0.15 to 0.3

14 to 28
14 to 28
+++ Low 3
triticonazole + chlorothalonil (Reserve)* 3.2 to 4.5 refer to label +++ Low 3/M5

1Other trade names with the same active ingredients are labeled for use on turfgrasses and can be used according to label directions.
2Units are oz, fl oz, or lb depending on formulation. 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.
3Use shorter intervals when conditions are very favorable for disease.
4Fungicide Resistance Action Committe code. Products with same code have the same mode of action and are in the same chemical class.
* 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

Species Data

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Red Thread stand symptoms

Figure 1. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 2. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 3. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 4. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 5. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 6. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 7. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 8. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 9. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 10. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 11. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 12. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 13. Red Thread stand symptoms.

Red Thread stand symptoms

Figure 14. Red Thread stand symptoms.

Red Thread foliar symptoms

Figure 15. Red Thread foliar symptoms.

Authors

Extension Coordinator
Entomology & Plant Pathology
Associate Professor and Extension Specialist (Turfgrass Pathology)
Entomology & Plant Pathology

Find more information at the following NC State Extension websites:

Publication date: Nov. 14, 2017
Revised: Dec. 16, 2019

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 in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. 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 local N.C. Cooperative Extension county center.

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