Wet soil conditions earlier this year were favorable for early infection with Sudden Death Syndrome (SDS). Heavy rains during flowering are also favorable for development. The first signs of SDS appear as scattered yellow or white spots on the leaves in the upper canopy. In the intermediate stage, these spots eventually coalesce to form brown streaks between the veins (interveinal necrosis) (Figure 1). On these leaves only the midvein and major lateral veins remain green (Figure 2). As the disease reaches the more advanced stages, premature defoliation occurs with petioles (leaf stems) remaining on the plant.

The progression from early symptom to defoliation will occur rapidly (less than 14 days in most cases). Symptoms of SDS can be confused with those of brown stem rot. To differentiate the two, split the stems of infected plants and check for discoloration. If the pith (center stem) is discolored, this is a symptom of brown stem rot. With SDS stem discoloration will be confined to the outer stem layers (vascular tissue) and can extend up the stem of infected plants. In addition to above ground symptoms, plants with SDS typically will have a rotted tap root and plants will pull easily. Upper lateral roots often are not affected.

The best action at this time is to identify these and other problems correctly so that you can develop a management strategy the next time soybeans are grown in the field. No action can be taken at this time to reduce the effect of SDS. As with any disease, to properly manage it the correct diagnosis is critical.

Diagnosis & Resources

If you are uncertain of the cause of damage in your field, I encourage you to have it identified at the University of Nebraska Plant and Pest Diagnostic Clinic.

More information on these and other soybean diseases can be found in the Soybean Disease Management section of CropWatch and on SoyCal.