Seeing yellow spots in your soybeans?

Are you seeing yellow-ish spots showing up in your soybean fields, especially in compacted parts of the field? This could be the start of Sudden Death Syndrome (SDS). With how wet its been there year, we've had the ideal conditions for disease development. 

Foliar symptoms of SDS, which look similar to foliar symptoms of BSR.

I've been in a few fields were you can start to see SDS symptoms appearing. I'm mainly seeing it in early planted soybean fields so far. Infected plants will have yellow spots between leaf veins early on. As the disease develops the spots will grow and form large chlorotic and necrotic blotches between leaf veins.  The leaf will remain green around the midvein and major lateral veins. 

You need to be careful though because the foliar symptoms of SDS also look similar to the foliar symptoms you may see with Brown Stem Rot (BSR). To be sure which disease you are seeing, split the stem. If the pith is white, then its likely you have SDS. If the pith is brown, then you have BSR. You can also check the roots. Plants with SDS will have root rot where as BSR does not cause root rot. 

(Left) SDS-infected soybean plant will have a white pith. (Right) BSR-infected plant will have a brown pith.

Unfortunately there is nothing you can do for SDS now, but you can start thinking about what to do to help in the future. Talk with your seed dealer about variety selection and even what seed treatment options are available. Planting date might be another factor as SDS is mostly showing up in the earliest planted soybeans. Soil compaction is another big item; elevating compaction may help decrease the severity of SDS. 

Daren Muller and Tristan Mueller published an ICM article a few weeks ago that discuss soybean diseases that are showing up this here. Other diseases that I've seen in SE/South-Central Iowa (in isolated areas) include: frogeye leaf spot, bacterial blight, and septoria brown spot, as well as some viruses.