Sudden death syndrome (SDS) is one of the leading yield-limiting soybean diseases in North America — in 2025 alone, SDS was responsible for over 49 thousand bushels of soybean yield loss in the United States. 2025 saw the greatest yield loss from SDS since 2014, likely due to wet weather conditions creating an ideal environment for sudden death syndrome development and toxin uptake.¹ The first step to managing SDS is proper identification. Timely scouting based on environmental conditions that historically favor disease development is important to set yourself up for successful management.
What is soybean sudden death syndrome?
SDS is primarily a root disease but typically also affects leaves and causes defoliation. SDS often occurs in fields where soybean cyst nematode (SCN) is present. Soybean sudden death syndrome is most severe when soybeans are planted into cool, wet soils, and/or when midsummer rains saturate the soil.
What causes sudden death in soybeans?
SDS is caused by the soilborne fungus Fusarium virguliforme. The fungus survives the winter in both corn and soybean residue as well as in the soil. It can infect soybean roots as soon as one week after crop emergence and in its early stages is usually restricted to the roots and stem near the soil line. During the late vegetative and early reproductive stages, toxins produced in the roots then move to the leaves, causing SDS’s characteristic foliar symptoms.² The SDS pathogen spreads from field to field with movement of the soil on equipment, field activity, birds, animals and any soil movement by wind or water erosion.
SDS diagnosis: distinguishing from BSR
Diagnosing SDS can be challenging as other diseases can cause similar symptoms. SDS foliar symptoms are identical to those caused by Brown Stem Rot (BSR), but BSR also includes brown pith in the stem that is visible when stems are cut lengthwise. With SDS, infected stem pith is typically white. So it is important to evaluate stems and roots, as foliar symptoms of SDS are not enough to make a definitive diagnosis. Dig up the plants and inspect them closely to confirm it is SDS.
What does SDS in soybeans look like?
The first symptoms of SDS typically appear on soybean leaves in late July or early August. Here’s what to look for when diagnosing SDS:
Above-ground symptoms include:
- Yellow blotches that form between the veins of soybean leaflets. These blotches expand between the veins, eventually appearing as brown lesions surrounded by other chlorotic areas.
- Leaves that may be cupped or curled, eventually leading to dead leaflets.
- Heavy SDS pressure may cause leaflets to drop off, leaving the petioles attached.
- Plants will dislodge from the soil easily because of decayed lateral roots and taproots.
Underground symptoms include:
- Grayish or brown discoloration of the taproot when split open. Split the stem and inspect the pith of the plant. If it is white with rotted roots, it is SDS. If the stem is discolored, it is more likely brown stem rot (BSR).
- Small, light blue patches indicating fungal growth on taproots and stems below the soil surface, especially if plants are already exhibiting advanced foliar symptoms.
Experts are available to help you make your diagnose of soybean sudden death syndrome. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
Endnotes
- “Soybean Disease Loss Estimates from the United States and Ontario, Canada — 2025.” Crop Protection Network, 6 Mar. 2026, cropprotectionnetwork.org/publications/soybean-disease-loss-estimates-from-the-united-states-and-ontario-canada-2025. Accessed 15 Apr. 2026.
- Jardine, Douglas J. “Sudden Death Syndrome.” Soybean Research & Information Network, May 2020, soybeanresearchinfo.com/soybean-disease/sudden-death-syndrome/. Accessed 15 Apr. 2026.
