Sudden Death Syndrome (SDS) of Soybeans

When initial foliar symptoms appear, the roots of SDS affected plants appear almost normal on the surface. But internally, a reddish-brown discoloration develops near the central core of the tap root and radiates outward and upward. The discoloration of the internal tap root tissues away from the central core become a streaky to uniform, light brown to light gray color. This discoloration spreads into the cortical tissues of the lower stem as the disease progresses. Pith tissues in the stem remain a normal white to green color which aids in the differentiation of SDS from brown stem rot. Root systems are often badly deteriorated.

Yield reduction due to SDS is dependent upon cultivar, weather conditions, time of disease onset, and severity of disease within a field. Yield losses result from premature plant death, pod abortion, lack of pod fill and low test weight.

SDS is caused by a soil borne fungus, Fusarium solani, form A (the "blue strain"). This strain of the root infecting fungus produces a toxin that is translocated from the infected taproot to the leaves and causes the obvious dying of leaf tissues. SDS has previously occurred primarily in areas where the Soybean Cyst Nematode (SCN) is a major concern. Root damage by the nematode does enhance SDS severity, but the presence of the nematode is not required for SDS to occur.

While SDS controls are limited, the following should help:

1. Plant as late in the spring as possible or at least stagger planting dates between or even within fields.
2. Plant soybean varieties representing more than one maturity group; do not plant a large portion of your acreage to a single variety.
3. Plant varieties which have performed well when SDS is present.
4. Manage SCN, maintain adequate soil fertility, and avoid crop stress.
5. Improve drainage in poorly drained fields and avoid compacting soils with farm equipment.
6. Crop rotation is advisable. SDS severity is greatest in continuous soybean production.
7. Harvest fields with any SDS in a timely fashion.

With extremely late planting of soybeans in areas of the state where SDS has previously been reported, symptom development may not occur until late August. Yield losses have not been as great in late planted beans; however, it is important to determine if the symptoms noted are those caused by SDS, Brown Stem Rot or a combinations of SDS and other late season diseases.