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Sudden Death Syndrome of Soybean
Causal Agent:
Foliar symptoms become visible in the early reproductive stages of soybean development (R1-R6).
Early foliar symptoms. Pale yellow spots develop between veins.
Severe foliar symptoms of SDS. Interveinal areas become entirely necrotic and leaves will drop prematurely.
Symptoms and Signs:
Symptoms most often occur in the crown, roots, and foliage. Infection is usually first identified as small yellow spots between the veins of the upper leaves of the plant at the time of flowering. The spots will expand rapidly into brown lesions with chlorotic halos until the entire leaflet becomes necrotic. Leaves will drop, leaving the petiole attached to the stem. Symptoms are most commonly seen at pod-fill stages (R3-R4). Characteristic blue-green spores may be visible on the taproot. The pith will retain a healthy appearance as opposed to brown stem rot, which can produce similar foliar symptoms, but will have a tan to dark brown pith.
Blue-green sporulation is sometimes visible on the taproot.
Disease Cycle:
Various spore stages of F. virguliforme overwinter in the soil for multiple years, leaving the possibility for large areas of a field to contain the pathogen even if non-host rotation is implemented. The fungus will begin colonizing the roots soon after planting. Between R1 and R6, the pathogen will grow deeper into root tissues and begin to produce toxins. Foliar symptoms will become visible at this stage. Leaves and pods may drop, containing hundreds of spores for overwintering to the following growing seasons. Heavy spring rains will cause higher infection rates and higher yield losses where the pathogen is present.
Disease Management:
Seed treatments- There are fungicides available for seed treatment for both SDS and SCN. Consult with your local extension agent and the current fungicide list (Ohio Soybean Diseases) to identify which seed treatments may work well in your system.
Plant resistant varieties- Use high-quality seed with resistance to both SDS and SCN. Resistant varieties should always be used in fields with history of these diseases. Resistance to SDS is quantitative, meaning different varieties will show varying levels of resistance. To measure this resistance, each company will have their own rating scale to measure the level of resistance found in each variety. For example, DuPont Pioneer uses a scale from 1-9 where 1=poor resistance and 9=excellent resistance. Rating systems are particular to each company, so be sure to identify the meaning of each rating before selecting varieties for the season.
SCN management- In many instances, fields in Ohio with SDS also have measurable levels of SCN. Crop rotation with a non-host or less susceptible host is ideal to reduce populations of SCN. However, corn, ryegrass, and wheat may serve as asymptomatic hosts of F. virguliforme. Monitor SCN populations by sampling and submitting soil for SCN counts (See SCN Fact Sheet).
Cultural practices- Planting when soils are warm, improving soil drainage, and reducing soil compaction will all help prevent SDS infection from occurring. SDS is most severe when soybean is planted in cool (<60°F), wet soils and has delayed emergence. Planting later in the spring when soils are warmer can help slow or eliminate SDS infection. Planting earlier maturing varieties is also thought to reduce the impact of this disease.
Wet soils provide a conducive environment for F. virguliforme. In order to reduce the incidence and severity of SDS, improve drainage either through the use of drainage tile or tillage.
SDS is often found in the areas of the field that are most compacted such as field edges and lanes.