Sudden Death Syndrome is a major cause of yield loss across much of the soybean acreage in the United States. As a part of an annual monitoring program by university researchers started 20 yeas ago, researchers have tracked the rise of SDS. According to the study, SDS is second to only soybean cyst nematode in contributing to soybean yield loss. In 2014, the damage caused by SDS cost soybean growers more than 60 million bushels in lost yield. When the top three soybean diseases (SCN, SDS and seedling diseases) are considered collectively, researchers found they represented a yield loss of nearly 250 million bushels. At this point in time, some researchers suggest that the severity of SDS this year could be as bad or even worse than in 2014. Some early scattered SDS symptoms are beginning to appear.
Early symptoms of SDS are mottling and mosaic of the leaves. Later, leaf tissue between the major veins turns yellow, then dies and turns brown. Soon after, the leaflets die and shrivel.
In severe cases, the leaflets will drop off, leaving the petioles attached. These symptoms are identical for three different diseases. The leaf symptoms produced by SDS are also the same leaf symptoms produced by BSR and stem canker. In order to definitely determine which disease is in your field you need to pull plants, split the lower part of the stem and examine the inside of the stem. This is the only way to differentiate which disease is present. The key traits to differentiate each disease are:
SDS -- When split, the lower stem and taproot of a plant infected with SDS will exhibit a slightly tan to light-brown discoloration compared to a healthy plant. The pith will remain white or slightly cream-colored.
BSR -- Brown stem rot darkens the pith, but there is little discoloration of the cortex.
Stem Canker -- Stem Canker will produce lesions at the nodes on the lower portion of the plant.
If you see the symptoms of SDS in your field, the critical thing to do is to determine which disease is causing the problem. By verifying the cause of the problem, you will be able to make better variety choices for next year. There are varieties that are less sensitive to SDS. There are varieties that are claimed to be resistant to BSR. I have not seen enough stem canker in this area for it to appear to be a concern. There are no soybean varieties that are highly resistant to SDS. There is a new seed treatment to provide protection for soybean seedlings against the fungus that causes SDS. Disease resistance is very difficult to screen for and measure. Look at your neighbor's fields and if they are clean, try to determine what factors may have prevented the disease.
There is nothing you can do to control the disease now. It is also likely that the scope of the disease will increase for the rest of the season. The diseased and dying plants will also be more susceptible to pod and stem blight, especially if we see regular or excessive moisture.
The damaged plants will have smaller seed and be more prone to shattering loss. If your fields have significant disease damaged plants you may want to harvest earlier to prevent seed loss and maintain seed quality. If you want any help in identifying the disease or have questions, contact your local extension office.