- Sudden Death Syndrome (SDS) infects soybean roots in the spring under cool, wet conditions.
- Additionally, rainfall events during the early reproductive soybean stages may have triggered toxin movement and sequential development of foliar symptoms.
- SDS symptoms appear later in the growing season and include interveinal chlorosis/necrosis and distinctive blue colonies on the tap root.
- Yield loss impacts depend on timing, prevalence, and severity of infection.
- Management options include variety selection, SCN management, and seed treatments.
Pathogen Biology and Symptoms
Sudden Death Syndrome (SDS) is caused by the fungus Fusarium virguliforme. Favorable conditions for SDS infection and development is denoted by two distinct periods: 1) infection of soybean roots in the early spring, and 2) significant rainfall during flowering. SDS infects soybeans in the spring under cool, wet soil conditions that are often associated with early planting. These conditions were prevalent in the spring of 2020. Infection is accentuated by the presence of soybean cyst nematodes (SCN), which injure the root system during feeding and create a point of entry for the SDS pathogen.
If conditions are relatively cool and wet during soybean flowering, the initial infection further develops and advances into the conductive tissues of the roots and lower stem and can be denoted by the blue-pigmented fungal colonies on the taproot (Fig. 1). The fungus then produces a toxin that is translocated into the upper foliage, causing interveinal chlorosis and eventually necrosis (Fig. 2). Visible symptoms typically appear in patchy distribution after flowering in July or August. The foliar symptoms are not distinct and may be confused with brown stem rot and other foliar diseases. Affected leaflets typically fall off, but the petioles remain attached to the stem. The stem pith remains white, but the cortical tissue may develop a faint grayish or tan discoloration, seen in cross-section or longitudinal slices (Fig. 3).
SDS can cause premature defoliation and reduced photosynthetic surface area for pod fill, which leads to fewer and smaller seeds. Yield losses from SDS can be substantial and tend to increase with the following factors:
- History of SDS in the field
- Continuous soybeans
- Susceptible variety
- Early planting
- Compacted soils
- Poorly drained soils
- Cool, wet soils early, followed by rainfalls during flowering
- Presence of SCN
- Early appearance of foliar symptoms
Management of SDS is entirely preventive. There are no effective “rescue” treatments once foliar symptoms become visible. Selecting a soybean variety with known partial resistance to SDS is an option. While short rotations of corn and soybeans may not reduce SDS pathogen load in subsequent soybean seasons, however, research has shown that extending the rotation with cereal grain such as wheat may help. Researches shows that reducing soil compaction, improving soil drainage, and maintain optimal soil fertility can reduce SDS. The use of a preventive specialized SDHI seed treatments such as ILeVO™ (BASF) or Saltro (Syngenta) can help delay the onset of foliar symptoms and minimize yield impacts. Also, take measures to manage and reduce SCN populations in the same fields. For more information on SDS sampling and management contact your local FS crop specialist.
For further reading, please see the following:
Figure 1. Symptoms of SDS on soybean roots. Note blue fungal colonies (Source:GROWMARK, Inc.).
Figure 2. SDS foliar symptoms (Source:GROWMARK, Inc.).
Figure 3. SDS symptoms in soybean stem.Note brown cortex, normal pith. (Source:GROWMARK, Inc.).