September 9, 2013

Figure 1. To differentiate between brown stem rot and sudden death syndrome, split the stem. With brown stem rot, shown above, the center of the stem will be discolored and typically will be brown from the soil line upward.

Figure 2.  Foliar, stem and crown symptoms of sudden death syndrome are shown here. Foliar symptoms for sudden death syndrome and brown stem rot can be similar.  Note differences in base of stems between Figures 1 and 2.

Sudden death syndrome was recently confirmed in soybeans in the southeast, central, and east central districts of Nebraska. A soil-borne fungal disease, SDS produces a very resistant survival structure that is not affected by crop rotation.

Research at Iowa State University has shown that the SDS pathogen also survives well on corn kernels on the soil surface. This is relevant to Neraska producers who have had SDS in their fields and this year experienced late season hail with grain loss. These kernels could serve as a site for this and other fungal pathogens to overwinter.

SDS was first confirmed in Nebraska in 2004 and often is contained to areas within a field. Brown stem rot has been a disease of Nebraska soybean for many years.

Differenting SDS and Brown Stem Rot

Foliar symptoms of SDS are similar to those of brown stem rot; however, stem damage is different. Split the stem to more closely exam symptoms.

With brown stem rot (Figure 1) the center of the stem will be discolored and typically will be brown from the soil line upward. With sudden death syndrome discoloration will be confined to the outer layers of the split stem. The center will not be discolored, but the root cortex will be light gray to brown and may extend up the stem (Figure 2).

As with many plant diseases, the main management option is to select resistant varieties. Correct diagnosis is important so you’re aware of the pathogens in this year’s crop that may overwinter and cause problems for next year’s harvest. Fields with high SDS should not be planted early in future years and should be managed to reduce any compaction issues. Rotation will not affect SDS. Fields with brown stem rot will benefit from longer rotations. Foliar fungicides are not recommended for managing either disease.

Resources

For more information on this disease see:

• Good Harvest in Corn Should Help Manage Soybean SDS by X.B. Yang and S.S. Navi, Department of Plant Pathology, Iowa State University
   
• Answers to Questions about Soybean Sudden Death Syndrome in Iowa 2010 by Alison Robertson and Leonor Leandro, Department of Plant Pathology, Iowa State University

For assistance in correctly identifying these diseases, submit a sample to the UNL Plant and Pest Diagnostic Clinic

Loren Giesler
Extension Plant Pathologist
Kevin Korus
Manager, Plant and Pest Diagnostic Clinic