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Scout for Sudden Death Syndrome of Soybeans (08/27/20)

Berlin Nelson was scouting soybeans in Richland County last week and identified multiple fields with Sudden Death Syndrome (SDS).

Berlin Nelson was scouting soybeans in Richland County last week and identified multiple fields with Sudden Death Syndrome (SDS). The disease was first confirmed in the state in 2018 (Richland County), it can cause significant yield loss, and may be occurring in other areas in North Dakota; particularly in the southeastern corner of the state. We recommend soybean growers scout for SDS.

What is Sudden Death Syndrome?

Sudden Death Syndrome in soybeans refers to a very specific disease that impacts soybeans, and is caused by the fungal pathogen Fusarium virguliforme. Frankly, the name is somewhat misleading; the disease is not generally ‘sudden’ and may not cause ‘death’. Other diseases (such as Phytophthora or Pythium root rot) cause damage more that is often ‘sudden’ and results in complete ‘death’. Thus, it is important to look for symptoms specifically related to Sudden Death Syndrome (below).

The pathogen is a root rot pathogen that can survive in the soil for several years. The pathogen infects soybeans soon after planting, and wet conditions favor development of the disease. The pathogen will cause root rotting, but also produces a plant toxin that moves up from the root tissue into the rest of the plant, causing foliar symptoms.

What are the symptoms and signs of SDS?

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.

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). Soon after, necrotic areas between the leaf veins occur, often bordered by a relatively thin yellow halo (Figure 3). With time, the necrotic areas coalesce, leaving only the veins of the leaves green. In severe cases, leaves may drop, but leaving attached petioles to the plant.

Examination of stem and roots tissue is very important to distinguish SDS from other diseases. 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 4). Brown stem rot (BSR) causes a look-alike leaf symptom, but the lower stem symptoms will be opposite; the pith will be brown and the other tissue will be white, giving it a ‘lead in a pencil’ look (Figure 5). Occasionally, a blueish fungal mold may be visible on the stem at the soil line of infected SDS plant (Figure 6).

Where do I scout for SDS?

We have only confirmed SDS in Richland County, however, it is possible (perhaps likely) that the disease may occur in other locations. The presence of soybean cyst nematode increases the likelihood that SDS develops and causes yield loss in your field (another reason to sample for SCN – see previous articles).  The SDS pathogen is soil borne, and moves whenever soil is moved (equipment, wind, water, etc..), so is first likely observed in areas where soil may be introduced into a field.

What do I do if I find it?

If you suspect SDS, it is worth confirming; the pathogen will survive for several years in the soil and management tools can be used in future soybean crops. Additionally, Dr. Berlin Nelson will be doing laboratory confirmations this fall. Please contact him directly if you are interested in submitting a sample (email below). It is important to remember that the pathogen only lives in the roots (a toxin causes foliar symptoms), so even though leaves look bad, confirmation can only be done with root tissue.

There is nothing that can be done to manage the disease this current growing season, but partially resistant varieties and/or fungicide seed treatments may help manage the disease in the future. Lastly, if you find SDS, it is important to also soil sample for SCN this fall (previous article). The two are tightly linked, and managing SCN will help manage SDS.

Where can I find more information?

Many excellent resources to identify and manage SDS exist. We recommend starting with:

The NDSU/UMN Soybean Disease Diagnostic Card series

and the ‘Sudden Death Syndrome’ publication by the Crop Protection Network (a multi-state group of Extension pathologists) as excellent resources to help identify and distinguish SDS from other diseases/ailments.

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Berlin Nelson

Soybean Pathologist

 

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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