Mitigate Sudden Death Syndrome with Proper Soybean Seed Selection

• Vascular-clogging toxins cause yellow flecking associated with Sudden Death Syndrome.
• Ideal soybean growing conditions lend themselves to SDS.
• Soybean cyst nematodes can exacerbate SDS.

Q. What is Sudden Death Syndrome, and how do you identify it?

A. Abigail Peterson, director of agronomy, Illinois Soybean Association: Sudden Death Syndrome (SDS) is a disease caused by a soilborne fungus, Fusarium virguliforme, that can survive in both corn and soybean residue systems. This fungal infection starts at soybean germination and is more prevalent in cool, wet growing conditions. The disease usually forms during the early reproductive stages. Growers sometimes misdiagnose SDS due to its resemblance to brown stem rot or stem canker. When scouting during the later vegetative stages, also known as the early reproductive stages, you’ll first notice leaf discoloration, which can range from yellow to brown. To eliminate the overlap of brown stem rot’s similar foliar symptoms, check the plant’s root. At the base of the plant, occasionally you will see a blue mold on the outside of the taproot – a sign of SDS. A final scouting step is to split the stem and evaluate if the internal tissue is discolored.

A. Dale Ireland, technical product lead, Syngenta: SDS is a “top five” soybean yield destructor – and has been for many years. It is an environmentally driven disease caused by Fusarium virguliforme, a commonly found soil fungus. Soy growers know the classic foliar yellow flecking is actually not the disease itself, but it is caused by F. virguliforme toxins produced in the root, plugging the vascular system within the soy plant. These toxins don’t allow proper nutrient flow between the root system and leaf canopy. The yellow flecks in the leaves coalesce and destroy much-needed leaf area during pod fill – often significantly impacting final yield.

Select soybean varieties with high-yield potential and with strong SDS scores.

Q. Do certain environmental conditions increase the likelihood of this disease?

A. Ireland: Environmental conditions highly impact SDS. An ideal SDS season begins with early planting in cooler, wetter conditions followed by a high-yield environment through much of the growing season. Some stress during early pod fill can create a load on the plant roots to deliver moisture and nutrients to the leaves, and this in turn increases the Fusarium virguliforme root infection toxins. Yellow flecks begin showing and coalescing and destroying leaf area, which is vital as it acts as a photosynthetic factory – producing what a plant needs to develop young soybeans in pods.

A. Peterson: Cool, wet soil conditions are usually a prime environment for SDS. The slowed germination from these conditions allows the fungus to infect the soybean roots. Wet conditions are a conduit for many soybean fungal diseases. SDS is unique in that its impact to a given area can be varied and unpredictable. Fields with a history of soybean cyst nematode usually have a correlation to SDS presence.

Q. When should growers be on the lookout for SDS?

A. Ireland: SDS typically begins showing up in spots – often field headlands or field entrances or compacted soil areas – in August. The earlier these symptoms show, often the greater the yield impact.

A. Peterson: It’s hard to predict or know the chance you’ll have the disease because SDS sometimes occurs later in the season. Know your field disease history and take good records of specific disease problems. Scout fields to accurately diagnose the problem. Detection from aerial plant health images can be a source of notification, although leaf tissue may be further intensified at that time than if you spotted it earlier during routine ground visuals. Also, contact your agronomist to check how products affect the health of your leaf tissue.

Q. What can growers do to mitigate this disease?

A. Peterson: SDS-infected fields can result in flower and/or pod abortion. Planting during warm, dry conditions isn’t always easy, but can help reduce SDS infection. It may help to plant historically SDS-prone fields later. Management practices that increase soil aggregation, reduce compaction, increase residue breakdown, and minimize soil loss can all reduce the risk of SDS. When reviewing varieties, choose soybeans that score well for both SDS tolerance and soybean cyst nematode resistance. Although SDS is associated with leaf tissue symptoms, a foliar fungicide will not affect a disease that infects the root system. To help reduce yield loss, evaluate seed treatments that have data provided from trials shown to protect yield in SDS conditions.

A. Ireland: Select soybean varieties with high-yield potential and with strong SDS scores. Managing your plant parasitic nematodes will help protect against SDS, too. Nematodes open the root system for Fusarium virguliforme infection and stress plants, leading to worse SDS infections. Another option is adopting a seed- and plant-safe seed treatment, like Saltro^®, that protects against SDS and nematodes. Rotating away from continuous soybeans also helps. Not managing SDS leads to more SDS. Because Fusarium virguliforme can establish itself in soils, if you choose to ignore SDS, the longer you grow soybeans, the greater the chances of SDS becoming established and turning into a perennial problem.