Gaeumannomyces graminis (take-all on St. Augustinegrass)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Sordariomycetes
Subclass	Sordariomycetidae
Family	Magnaporthaceae
Genus	Gaeumannomyces
Species	Gaeumannomyces graminis

Scientific Name

Gaeumannomyces graminis var. graminis

Common Name

take-all root rot

Author: Clarissa Balbalian, Mississippi State University

Reviewed by: Maria Tomaso-Peterson, Mississippi State University

Pathogen

Gaeumannomyces gramnis (Sacc.) Arx & D. Olivier var. graminis is a filamentous ascomycete fungus causing root and crown rot diseases in the Poaceae family, including take-all root rot of St. Augustinegrass (Stenotaphrum secundatum).

Dark brown to black runner hyphae are septate and 4-7 μm wide. Branching hyphae are paler brown, have a more meandering growth habit and develop brown, lobed, terminal hyphopodia 15-25 μm by 10-20 μm on side branches that can be up to 40 μm long. Branching hyphae also may have simple, unlobed, terminal or intercalary hyphopodia that measure 7-15 μm by 4-7 μm.

Perithecia are embedded, black globose to oval 200-400 μm in both diameter and length, and 150-300 μm wide. Asci are unitunicate, elongated clavate, 80-130 μm by 10-15 μm and contain 8 hyaline to faintly yellow ascospores when mature. A small apical ring 2.5-3.0 μm is visible as 2 small refringent dots in side view. Ascospores are slightly curved, 80-100 μm by 2.5-3.0 μm, with rounded ends and taper toward the base. Mature ascospores have 3-5 often indistinct septa. Paraphyses are 8-10 μm wide at the tip, are longer than the asci, are hyaline, and often are constricted at the septa.

Hyaline, unicellular, slightly to strongly curved phialospores 4-7 μm by 1.0-1.5 μm are often formed in culture. Phialospores are borne on phialides that are 9-18 μm by 2-3 μm, widest at the base and tapering to a thin apex. Phialides may be aerial or submerged, are slightly curved, hyaline to faintly pigmented, and may be clustered on the sides of hyphae or terminally.

Symptoms and Signs

Symptoms in a St. Augustinegrass sward first appear as irregular chlorotic patches that may range from a few centimeters to several meters in diameter. The patches gradually thin as the plants become brown and necrotic. On individual plants, the lower leaves are the first to become chlorotic. Roots with early infections are thin with isolated black lesions. As root infections progress, the roots become black and brittle, resulting in short, rotted roots. Dark brown to black lesions also appear on the stolons and nodes. The fungus typically presents on the roots and aboveground parts of the plant as hyphae with lobed hyphopodia. Perithecia, if present, are in the lower leaf sheath.

Ecology and Spread

Gaeumannomyces graminis var. graminis is a common component of the microbial population in warm-season turf settings and behaves as a pathogen on turf that is under stress. The fungus spreads from plant to plant via vegetative mycelium growing along roots and stolons, and infection occurs through hyphopodia. The fungus survives on infected plant material (roots and stolons) and can be spread by the movement of this material during sodding or sprigging, as well as by cultural management practices such as aerification and verticutting. The fungus is most active during cool, wet weather typical of spring and fall. Symptoms usually become obvious when the turf is under heat and drought stress in late spring or summer. Turf growing in conditions including: light sandy soils with low organic matter, a pH above 6.5 in the root-zone, unbalanced soil nitrogen and potassium, or manganese deficiency is very susceptible to infection.

Geographic Distribution

Gaeumannomyces graminis var. graminis has a widespread geographic distribution and has been reported infecting numerous hosts in the Poaceae from the United States (Alabama, Arkansas, California, Florida, Georgia, Illinois, Indiana, Louisiana, Mississippi, and Texas) as well as Africa, Australia, Bahamas, Cuba, Great Britain, India, Italy, Japan, Papua New Guinea, Philippines, and Sweden.

Management

Management of any pathogen is often dependent upon both cultural and chemical options. Consult your local extension specialist or agent for recommendations relevant to your particular host and state.

Cultural Management

Cultural practices that promote turf vigor and prevent infection are the key to managing take-all root rot. Proper mowing height is important to avoid undue stress to the turf. St. Augustinegrass should be maintained at a height of 2.5 to 3 inches. A soil pH of 6.0 to 6.5 is less favorable to the Gaeumannomyces fungus. Topdressing with sphagnum peat moss at a rate of 1 bale (3.8ft³) per 1000 ft² has been shown to provide protection for up to 2 years. The acidic pH of the peat moss (pH 4.4) is theorized to inhibit growth of the fungus on exposed stolons and roots. Soil fertility should be balanced and slow-release fertilizers used. Ideally nitrogen should be applied in a pound for pound ratio with potassium. Micronutrients, especially manganese, also should be monitored and supplemented as foliar applications in the sulfate form as necessary. Foliar feeding is necessary for turf with severely compromised root systems. In areas with compacted soil, core aerification is helpful. Cores should be removed and should not be used as topdressing. Do not place new sod directly over infected sod. Remove all infected plant material, including roots, prior to laying new sod.

Chemical Management

Chemicals are best applied preventatively and in conjunction with beneficial cultural practices. Chemical effectiveness is poor when stressful cultural conditions are present and disease pressure is high. Fungicide applications should begin a month before symptoms are typically observed and continue monthly, as long as environmental conditions are favorable for disease development. For best results, water fungicide applications into the root zone immediately following application. Active ingredients that are labeled for use on take-all root rot are listed in the table below.

Fungicide information compiled from various sources. Efficacy is categorized as Poor, Fair, Good, or Excellent.

Active Ingredient	Efficacy	Residential	Sod Farm	Athletic Field	Golf Course
Azoxystrobin	Good	X		X	X
Fenarimol	Fair			X	X
Myclobutanil	Fair	X			X
Propiconazole	Poor	X	X	X	X
Tebuconazole	Fair				X
Thiophanate-methyl	Fair	X		X	X
Triadimefon	Fair-Good		X		X

Remember: the label is the law.

Diagnostic procedures

The presence of dark runner hyphae and lobed hyphopodia are diagnostic of take-all root rot caused by Gaeumannomyces graminis var. graminis. The presence of lobed hyphopodia differentiates variety graminis from the other varieties of G. graminis. Necrotic roots and stolons can be surface sterilized, blotted dry on sterile paper and plated on SM-GGT7, a media selective for Gaeumannomyces-like fungi (2), or on Potato Dextrose Agar (PDA) amended with 100μg ml^-1streptomycin sulfate. PCR primers specific for Gaeumannomyces graminis var. graminis have been developed (5).

Resources and References

1. Colbaugh, P.F., E.A. Williams, J.A. McAfee, and J.J. Heitholt. 2005. Use of sphagnum peat moss topdressing to control take-all root rot of St. Augustinegrass (Stenotaphrum secundatum). INternational Turfgrass Society Research Journal 10, pp. 170-174. International Turfgrass Society.
2. Elliot, M.L. 1991. A selective medium for Gaeumannomyces-like fungi. Plant Disease 75:1075.
3. Elliot, M.L. 1995. Effect of systemic funigicides on a bermudagrass putting green infested with Gaeumannomyces graminis var. graminis. Plant Disease 79:945-949.
4. Martinez-Espinoza, A., D. Gardner, and J. Price. 2005. Management of Gaeumannomyces graminis (take all root rot) on St. Augustinegrass in coastal Georgia using fungicides and soil amendments. Phytopathology 95:S66.
5. Rachdawong, S., C.L. Cramer, E.A. Grabau, V.K. Stromberg, G.H. Lacy, and E.L. Stromberg. 2002. Gaeumannomyces graminis vars. avenae, graminis, and tritici identified using PCR amplification of avenacinase-like genes. Plant Disease 86:652-660.
6. Smiley, R.W., P.H. Dernoeden, and B.B. Clarke. 2005. Compendium of turfgrass diseases, third edition. The American Phytopathological Society, St. Paul, MN.
7. Walker, J. 1973. Gaeumannomyces graminis var. graminis CMI Descriptions of Pathogenic Fungi and Bacteria. Set 39, Sheet 381.
8. Wells, W., B. Layton, A. Henn, and J. Taylor. Establish and manage your home lawn. Mississippi State University Extension Service. Publication 1322.

Acknowledgments

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)