With a name like sudden death syndrome (SDS), this soybean disease certainly demands our agronomic attention. But, while it’s serious, understanding SDS might actually make it less intimidating.
Sudden death syndrome was first identified in Arkansas in the early ’70s, and has since spread to nearly every state where soybeans are grown. Typically, SDS seeks cool, moist soils, but despite a drier growing season so far this year, SDS has been showing up in some fields across various parts of the country. The disease is caused by the soilborne fungus, Fusarium virguliforme, which is actually already present in nearly every field where soybeans are grown. This fungus attacks the soybean’s roots early in the season.
Above-ground symptoms do not typically occur until the bean reaches the reproductive stages, but symptoms are visible and do not come on as suddenly as the name infers. Toxins accumulate in the roots, and during the reproductive stages are transported into the leaves as the plant attempts to rid itself of them. Leaf tissue between the veins turns yellow, then brown, and eventually, the leaves prematurely drop.
These visual symptoms of SDS are similar to those of brown stem rot, but there are important distinguishing characteristics. You can identify SDS by splitting the lower stem and distinguishing a dark cortex with a white to tan pith.
Unfortunately, in soybeans, SDS is favored by high-yielding environments and well-fertilized plants. Further, fungicide applications have not proven effective in battling SDS. High soil moisture during vegetative stages, poorly drained soils, compacted areas and the presence of soybean cyst nematodes (SCN) are all factors that increase the severity of SDS.
While there is nothing that can be done once SDS is detected, management decisions in the future can help limit losses. Some of these best practices include:
- Using seed varieties with better SDS tolerance, or choosing varieties that are resistant to soybean cyst nematodes. (Fields with a history of SCN tend to be more susceptible to SDS.)
- Delaying planting, or planting earlier-maturing varieties — which limits the plant’s exposure to SDS;
- Conducting deep tillage that removes soil compaction and improves soil drainage in low areas; and
- Adding another crop into the rotation, such as wheat.