Sudden death syndrome (SDS) is ravaging many Midwest soybean fields.

Farmers watched anxiously as low-lying areas of some fields suspiciously turned brown then watched those small areas grow into much larger areas of dying plants. SDS is showing up on a scale not seen since it hit Illinois soybean fields in the early 1990s. This year’s yield losses to SDS are expected to exceed 20 percent in some fields.

The cause of the disease is a soil fungus that is widespread throughout the Midwest. It infects the soybean root early in the plant’s development; later, the pathogen rapidly kills the plant during pod set and pod filling. Infection of the soybean root is worsened by cool, rainy weather throughout the first half of the growing season as well as soil compaction and poor drainage.

Development of SDS depends upon many factors including planting date, tillage, variety of soybean, and the presence of other stresses such as SCN. Early planted soybeans tend to be more heavily damaged than later planted beans because of the more favorable conditions for infection by the soilborne fungus.

The impact of tillage on SDS remains unclear. Reduced tillage, including no-till, may influence the presence of the disease because corn residue causes slower warming and drying of the soil. Corn residue, including dropped corn kernels, harbors the fungus that causes the disease, possibly increasing the amount of the fungus in the soil. However, mature no-till fields tend to drain more quickly than conventionally tilled fields reducing the saturated seed zones that promote infection of the root by the fungus.

Crop rotation is of limited value. University of Illinois researchers report finding SDS in continuously grown soybeans, soybeans following one or two years of corn, and in fields that had been out of soybean production for many years. They reported that the fungus that causes SDS can persist in the soil for many years even without a host crop.

SDS can be more severe in field areas also infested with SCN. Feeding by the nematode on soybean roots adds additional stress that often increases the impact and severity of SDS. Researchers have discovered that cysts can contain the fungal pathogen that causes SDS. However, the two problems are known to exist independently.

Farmers planting maturity group II and I soybeans may be at greater risk of seeing SDS in their fields because soybeans in those maturity groups generally have lower levels of field tolerance to the disease. Although public and private plant breeders are working hard to improve the plant’s performance against the fungus, it will be another 5 to 10 years before greater levels of protection are in place in those maturity groups.

Checkoff-funded researchers throughout the Midwest are working feverishly to solve the SDS problem. Emphasis is being placed on the development of breeding lines with improved tolerance to SDS and screening and categorizing the response of commercial soybean varieties.