Sudden Death Syndrome of Soybean Confirmed in South Dakota

Written collaboratively by Emmanuel Byamukama, Connie Strunk, Connie Tande, and Febina Mathew for iGrow.

Last week, sudden death syndrome (SDS) was confirmed in Lincoln, Turner and Union counties. Most of the fields found with SDS had very few scattered plants showing symptoms, with the exception of one field in Lincoln County which had a moderate level of SDS (Figure 1). These symptoms can be mistaken for maturing soybeans but a close-up look at the symptomatic plants will show typical SDS symptoms (Figure 1).

Figure 1. A soybean field with sudden death syndrome in Lincoln County (left) and a close-up of symptomatic leaves (right). Credit: E. Byamukama, 9/01/17

Symptoms

Sudden death syndrome is a fungal disease caused by Fusarium virguliforme. This pathogen survives in infested soybean residue and in the soil for several years. Planting in wet, cool soils in the spring promotes infection. The SDS pathogen infects soybean seedlings early in the growing season but symptoms do not appear until the early reproductive stages under cool temperatures and frequent rainfall conditions.

SDS symptoms start as small chlorotic spots on the leaves. These spots quickly expand leading to large yellow blotches which eventually become necrotic (dead leaf tissue) between the leaf veins, leaving vivid green veins (Figure 2). Infected plants have rotted roots. Splitting the stem lengthwise reveals the browned cortex and white pith which is a diagnostic characteristic of SDS. When the soil is moist, blue spores may be noticed on the taproot of infected SDS plants (Figure 3). In order to distinguish SDS from other root and stem rots such as brown stem rot, again split the stem and look for the discolored cortex near the tap root as well as white pith. Brown stem rot does causes the vascular tissues to be brown.

Figure 2. Beginning SDS symptoms (left) and advanced symptoms (right). Credit: E. Byamukama

Figure 3. Blue fungal growth on the taproot is a sign of Fusarium virguliforme, the pathogen which causes SDS. Credit: E. Byamukama

Management

There are no in-field treatments for SDS management. Since the SDS pathogen infects the soybean seedlings at planting, managing SDS should start before planting.

• SDS is favored by planting in cool wet soils in spring. Therefore plant when soils are warm and not excessively wet.
• Some fungicide seed treatments are effective at protecting seedlings from getting infected. Currently an active ingredient that has been tested and found to be effective against SDS is Fluopyram.
• Some cultivars are more tolerant to SDS than others. Consider SDS ratings in seed catalogue and plant SDS tolerant cultivars.
• Corn kernels can be survival surfaces for the SDS pathogen, therefore harvest corn cleanly.
• Manage soybean cyst nematodes (SCN). While not every field with SCN has SDS, presence of SCN may exacerbate SDS.
• Practice good agronomic practices such as crop rotation, fertilizer management, drainage and weed control to improve soybean crop development that assist the plants in withstanding disease infections.

This blog post is brought to you by the South Dakota Soybean Research & Promotion Council.