Soybean Sudden Death Syndrome
Soybean Disease Information Note 7
Stephen Koenning, Extension Plant Pathologist

Sudden death syndrome (SDS) is the common name for a root-rot of soybean caused by the fungus Fusarium solani f.sp. glycine. The disease was first found in North Carolina in 2001, although it may have been present earlier (Figure 1).  Yield loss in 2001 was negligible. The likelihood that major yield loses from SDS will occur in North Carolina is unclear, but SDS is a potentially serious disease.  Periodically this disease has been a problem in the mid-south and mid-west since the 1980's.  Most years the disease is of minor importance.  In years when disease symptoms are widespread and apparently severe, soybean yields are generally excellent.  The name "sudden death" refers to the early defoliation and death of the soybean plant.  The common name stems from the fact that in wet years, foliar symptoms seem to spread rapidly through a field at or after the pod filling stage. Disease is usually more severe in high yield environments. Sudden death syndrome is often associated with the soybean cyst nematode, Heterodera glycines. See Soybean Disease Information Note #1 for more information.

Symptoms

Foliar symptoms of soybean sudden death syndrome resemble those caused by several other plant pathogens and or damage from certain insects (Figures 2 & 3). Red crown rot (black root rot), phytophthora root rot, charcoal rot, stem canker, brown stem rot, southern blight, and occasionally, damage from dectes stem borer (an insect) may also cause leaf symptoms that resemble SDS (see Soybean Disease Information Note No. 5 - Identification and Management of Mid-to-Late Season Soybean Stem and Root Rots, or the Soybean Disease Atlas). The symptoms associated with red crown rot, caused by Cylindrocladium parasiticum (the same fungus causes CBR in peanut), are virtually identical to those found with sudden death syndrome caused by F. solani.
Foliar symptoms of sudden death syndrome typically do not appear prior to soybean flowering. Early symptoms at the R3 and later growth stages, if present, are only chlorotic (yellow) spots on the leaves between veins (Figure 2). As the soybean plant progresses to the pod forming stage these yellow spots may coalesce, becoming yellow between the veins which remain green. Leaves may become crinkled, resembling virus infection. As disease progresses further, the yellow between the veins will become brown (necrotic) as the tissue dies (Figure 3). Roots will exhibit an obvious root rot and plants can be easily pulled from the soil. Splitting the stem with a sharp knife will reveal a brown to reddish-brown discoloration of the lower stem and root. The discoloration of the vascular elements, usually will not extend more than an inch or two above the soil line (Figure 4).The pith will remain white, unless other diseases such as phytophthora root rot or charcoal rot are also present. Pods may be aborted and plants may defoliate early. Often, defoliated plants will retain their petioles. Retention of the petioles is a symptom frequently associated with SDS, but less commonly with red crown rot of soybean). Symptoms on the root system are difficult to distinguish from other soybean root rots. Typically the causal fungus must be isolated in a lab and the pathogen identified under a microscope. Occasionally the fungus will form masses of white spores on the roots that may become blue to blue-green as they mature. (Figure 5). Correct identification of disease is important in formulating a management strategy.

Diagnosis

As mentioned earlier, a number of pathogens cause symptoms that resemble SDS. Red crown rot, in particular, has symptoms that are virtually identical to SDS. Often it will be necessary to have the fungus isolated to be certain of the cause. Plant and soil samples can be sent to the plant disease and insect clinic through your North Carolina Cooperative Extension Service County Agent.

Sudden death syndrome is caused by the soil-inhabiting fungus Fusarium solani f.sp. glycine The fungus survives in the soil for numerous years and may be able to increase on other hosts. Crop rotation does not seem to affect disease severity, and sudden death syndrome has occurred following corn or cotton crops. Suppression of soybean cyst nematode through crop rotation or the use of cyst resistant soybean varieties may result in less disease. Infection of soybean roots by F. solani probably takes place shortly after soybean emergence. Wounds or changes in plant physiology caused by infection by plant-parasitic nematodes may increase the severity of SDS. Disease development is favored by high soil moisture. Symptom development may progress rapidly following cool weather. The fungus survives in decayed plant tissue and soil after the plant dies.
Because of the foliar symptoms, researchers have suggested that a toxin produced by the fungus induces these symptoms. The similarity of the SDS foliar symptoms to several other soybean diseases that affect the vascular system, however, suggests that symptom expression is probably a response of the plant to stress at pod filling.

Management

Recommendations for management of SDS is based on data developed in other states. Soybean varieties with moderate-to-high levels of resistance to SDS are available (Table 1). Growers are advised to check literature provided by their seed supplier for information on disease resistance. Varieties resistant to SDS should be considered in fields known to be affected by this disease. In choosing a variety, however, be certain that it has resistance to pathogens known to be present such as Phytophthora sojae, cyst or root-knot nematodes. Many new varieties and especially varieties in later maturity groups have not been evaluated for resistance to this disease.
Crop rotation does not seem to affect disease severity. Sudden death syndrome has occurred following corn or cotton crops. Nonetheless, growers should continue with rotations and or cropping systems that suppress population densities of plant-parasitic nematodes. Suppression of soybean cyst and (or) root-knot nematode through crop rotation or the use of soybean varieties resistant to the species and races of plant-parasitic nematode present may limit yield loss from SDS. An on-line aid in choosing varieties adapted to North Carolina with information on nematode resistance is available from the NCSU Department of Crop Science at: http://www.cropsci.ncsu.edu/soyvar/VarietyFilter.asp .

Sudden death syndrome tends to be more severe in fields under reduced tillage regimes. Late planting, as occurs with double cropping small grains and soybean or the use of early maturing varieties may also suppress disease development.

* Most of this information was obtained from the seed company catalogs and is based on limited trials conducted by University and company personnel. Many soybean varieties in maturity groups V-VIII have not been rated for this disease.

Other Resources

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Soybean Disease Atlas
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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 by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.

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Last update to information: January 2002
Last checked by author: January 2002
Web page last updated on January 2002 by Tom Creswell.