Sudden Death Syndrome has been showing up from late July into August, but it really got its start back on those cool damp days in May. X. P. Yang, an expert on the subject from Iowa State, says the plants actually got infected in after germination and during emergence when soil conditions are right. The fungus lives in the plant roots making its way into the xylem where it then gets transported throughout the plant.
Making the problem worse are soil compaction and the added stress of soybean cyst nematodes. The plant eventually looses its leaves and is unable to produce.
It will over winter in the crop residue and actually survives better on corn stalks than soybean residue so a corn beans rotation does not help.
Management practices include selecting tolerant varieties, improving soil drainage while managing soil compaction and SCN. It may also help to plant infected fields later to reduce risk of further infection of new crop.