NC State Extension Publications

Introduction

Soybean Sudden Death Syndrome (SDS) first appeared in Arkansas in 1971 and has since spread to almost every soybean producing state. Afflicted plants suffer from flower and pod abortion, reduction in seed size and vigor, and extreme yield losses. The severity of the symptoms depends on the maturity of the plant at the time of infection. SDS rarely affects plants in North Carolina, but losses are seen when infections are concurrent with soybean cyst nematode infections or cool, wet environmental conditions.

Soybean affected by SDS

Soybean plant affected by Sudden Death Syndrome caused by Fusarium virguliforme

Photo Courtesy of Dr Rachel Vann, NCSU Soybean Specialist

Pathogen and Life Cycle

The causal agent of Soybean Sudden Death Syndrome (SDS) is the soil borne fungus Fusarium virguliforme (formerly F. solani f. sp. glycines). F. virguliforme overwinters as chlamydospores (resting spores). The fungus begins attacking plants roots about 2-3 weeks after germination, but plant symptoms are not observed until later in the growing season. F. virguliforme reproduces by producing macroconidia to disperse throughout the soil and spread to new host plants. Once inside the plant, F. virguliforme produces toxins that cause plant symptoms.

Host Crops

Soybean (Glycine max) is the primary host for this pathogen. It can also infect alfalfa and results in similar symptoms to those found in soybean. Sugar beets and canola do not show symptoms when infected, but do have severely reduced biomass.

Symptoms and Identification

Symptoms begin in the roots and include necrosis and dieback, similar to other root diseases (Figure 1). The vascular tissue of the taproot becomes brown and discolored. This discoloration can extend upward to the lower stem, but does not invade much beyond a couple of inches above the soil line (Figure 2). Occasionally, blue-green masses of macroconidia may be visible on roots close to the soil line (Figure 3). Later in the season, usually after plants have flowered, the fungal toxin migrates up through the vascular tissue into the canopy. The leaves initially develop intravenous chlorotic spots that soon become necrotic (Figure 4). In the advanced stages of the disease, only the central vein remains green and leaflets begin to detach from the petioles.

Wilting and Chlorosis of Soybeans

Figure 1. Symptoms of wilting and chlorosis of soybean plants in a localized disease focus

Photo Courtesy of Dr Rachel Vann, NCSU Soybean Specialist

Vascular discoloration

Figure 2. Cross section of soybean stems revealing vascular discoloration of affected plants

Blue hyphae on soybean roots and crown

Figure 3. Blue hyphae on the surface of the crown and roots of affected soybean

Interveinal chlorosis and necrosis

Figure 4. Interveinal chlorosis and necrosis caused by Fusarium virguliforme

Photo Courtesy of Dr Rachel Vann, NCSU Soybean Specialist

Diseases with Similar Symptoms

SDS can be easily confused with other root rot diseases, including Fusarium wilt, Phytophthora root rot, and white mold.

The foliar symptoms caused by SDS can sometimes be mistaken for virus, like soybean vein necrosis virus (Figure 5).

SVNV soybean

Figure 5. Soybean Vein Necrosis Virus (SVNV) symptoms on a soybean leaf

Management

Crop Rotations

Rotation with wheat or oats reduce SDS damage the greatest of rotations assessed. Maize, cotton, sorghum and rice to not appear to reduce disease pressure and are not recommended. Rotations with at least two years out of soybean production are best in severely affected fields.

Resistant Cultivars

Planting cultivars with some resistance to the disease can help reduce symptom severity and improve yield.

Irrigation Management

Disease is worse in years with heavy rainfall or in fields with heavy irrigation. Limiting excess irrigation and improving soil drainage where possible will help to reduce disease losses.

Sanitation

Tools and farming equipment can spread the fungal spores between fields. Make sure all tools and materials rinsed of soil debris and sterilized with bleach or ethanol when moving to a different field.

Chemical Control

Seed treatments containing fluopyram work well against this disease, since the pathogen attacks the plant early in the season. Losses by SDS in North Carolina often do not warrant the use of chemical controls, but seed treatments containing fluopyram have had positive yield responses in seed treatment trials for SDS management.

Useful Resources

Acknowledgements

This factsheet was prepared by the NCSU Field Crops and Tobacco Pathology Lab in 2019.

Authors

Graduate Student
Entomology and Plant Pathology
Assistant Professor & Extension Specialist
Entomology & Plant Pathology

Publication date: May 8, 2019

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.