Sudden Death Syndrome (SDS) is showing up in many soybean fields in Iowa and parts of the Midwest. A problem since the 1970s, it has become a bigger threat in recent years. According to Dr. Alison Robertson, extension plant pathologist at Iowa State University, some studies suggest it may have to do with the weather, as it's dependent on environmental conditions.
"When we look back over the last three or four growing seasons, it has been wetter and cooler than normal, particularly at planting time and also somewhat later in the season," Robertson says. "Cool, wet temperatures favor infection by the fungus and development of the disease. That's why I believe we have seen an upsurge in disease development over the last few years."
While there's not a lot growers can do about SDS this far into the season, Robertson says producers still need to get out in the field to determine if they have an SDS problem.
"As you look across your field, you're going to see these yellow patches," Robertson says. "And a lot of times, these yellow patches might be in more compacted areas of the field. Then when you look at the leaves, in between the veins, the leaf tissue is yellow and then it becomes brown and it dies and falls off, leaving skeletons of leaves."
Robertson suggests inspecting soybean leaves and stems closely because it could be a different infection.
"Brown stem rot causes very similar leaf symptoms," Robertson says. "To tell the difference, you will need to split the stems of many plants, and if the pith (center) of the stem is brown, it means you have brown stem rot in that field. However, if the pith is white and you have quite a bit of root rot as well, you may be looking at SDS."
Robertson says identifying SDS is the first step to managing it. Knowing which fields have SDS this season will allow soybean growers to implement proper management practices the next time soybeans are planted.
"A grower could speak with his seed dealer because there are varieties that are more tolerant of the disease than others," Robertson says. "Another thing we know about the disease is there is an interaction with soybean cyst nematode. The higher the population of soybean cyst nematode, the higher the risk of developing SDS, which can develop early on in the seed fill period.
"Managing soybean cyst nematode is very important for managing SDS."
Another management practice Robertson suggests is to delay planting until conditions are more ideal.
"The other management recommendation, which is a little more difficult, is to avoid planting your soybeans if the soil is going to be cool and wet at the time of planting or anytime within that first week or so of planting."
SDS is caused by a soil fungus that can survive in the soil for many years. In fact, Robertson says recent research findings suggest the fungus can even survive on corn kernels, meaning a 2-year rotation between soybean crops may not manage, inoculate levels or reduce the risk of SDS."