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Sudden Death Syndrome (SDS) of Soybeans

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This page was adapted from the article, "Sudden Death Syndrome (SDS) of Soybeans," which appeared in Crop & Pest Report on August 25, 2022.

Sudden Death Syndrome (SDS) was first confirmed in the state in 2018 (Richland County), and in 2020 was confirmed hundreds of miles away in Cavalier County. We don’t know exactly how prevalent SDS is in the state, but the Richland and Cavalier County confirmations suggest it is more common the we think.  Additionally, the severity of SDS is tightly linked to the presence of soybean cyst nematode (see article below). You can certainly have SDS without SCN, but you are more likely to find (and suffer yield loss) from SDS if you have SCN.  I suggest you scout areas of your field known to have high SCN pressure.

The pathogen is a soil-borne root rot pathogen (Fusarium virguliforme) that can survive for several years.  The pathogen infects soybeans soon after planting, and wet conditions favor development of the disease. Thus, for infection to occur and disease to develop, that soybeans will have had to have some moisture. The pathogen will cause root rotting, but more importantly, produces a plant toxin that moves up from the root tissue into the rest of the plant. It is the plant toxin that causes the foliar symptoms.

SDS often shows up in fields in oval/circular spots or clusters of plants in a field (Figure 1).  When the disease is becoming severe, yellow patches of soybeans are often visible from a distance.

A soybean field with many areas where the plants have yellowing leaves.
Photo Credit:
Dr. Berlin Nelson
Figure 1. Area of a soybean field with Sudden Death Syndrome.

The first foliar symptoms of SDS are bright chlorotic (yellow) spots that occur diffusely (not connected to one another) between the leaf veins (Figure 2).

A closeup view of soybean leaves many of which have yellow spots and some that have brown spots as well.
Photo Credit:
Dr. Berlin Nelson
Figure 2. A mix of beginning and advanced foliar symptoms of Sudden Death Syndrome.

Soon after, necrotic areas between the leaf veins occur, often bordered by a relatively thin yellow halo (Figure 3).

Three sets of soybean leaves in a horizontal lean. The leaf set on the left has small yellow spots primarily on one of the three leaves. The leaf set in the middle has yellow coloring along the veins of all three leaves and brown coloring everywhere else on the leaves. The leaf set on the right has two leaves both are mostly brown and curled at the edges.
Figure 3. Progression of symptoms of Sudden Death Syndrome.

With time, the necrotic areas coalesce, leaving only the veins of the leaves green. In severe cases, leaves may drop, but petioles will remain attached to the plant (Figure 4).  

A soybean plant with some leaves with extensive yellow and brown spots and others that are completely brown and curled up.
Figure 4. Severe symptoms of Sudden Death Syndrome, including leaf drop (note naked petioles) and interveinal chlorosis and necrosis.

Examination of stem and roots tissue is very important to distinguish SDS from other diseases, particularly brown stem rot (see next article).  With a knife, scrape off the outside of the tissue of the lower stem and tap root near the soil line.  SDS infected stems have tanning or browning, but the pith (center of the stem) will remain white (Figure 5).

Closeup view of a soybean plant stem that has tanning and browning.
Photo Credit:
Dean Malvick, UMN, extracted from Soybean Disease Diagnostic Series, NDSU Extension Publication-1867.
Figure 5. Tan to brown soybean root tissue consistent with Sudden Death Syndrome.

 

Sam Markell
Extension Plant Pathologist, Broad-leaf Crops