By Alicia Harstad, Stutsman County Extension agent for agriculture and natural resources
Now is a good time to scout for late-season soybean diseases in order to manage them for future years. In particular, soybean cyst neonate (SCN), sudden death syndrome (SDS) and charcoal rot are economically important diseases for North Dakota. The first step to managing these diseases is to scout for their presence. The symptoms of these diseases are most noticeable toward the end of the growing season and are most prevalent in a hot and dry year.
A couple of weeks ago, I wrote an article about SCN. It is a very small, microscopic worm-like nematode that penetrates soybean roots, robbing the plant of nutrients and water. SCN can even reduce nodulation which is vital for nitrogen fixation of the plant, resulting in the soybean plant producing fewer pods and reducing yield. The best way to monitor for SCN is to soil sample this time of year to determine the nematode egg levels in the soil. The North Dakota Soybean Council funds a SCN soil testing program for NDSU Extension. Farmers are able to pick up soil testing bags at the Extension office and submit SCN samples for free. We still have SCN soil testing bags at the Stutsman County Extension Office. NDSU Extension creates a map of where SCN is in the state (farmer information is kept confidential) to help monitor where the disease is in the state.
Sudden death syndrome (SDS) of soybeans is a relatively new disease to North Dakota. It was first confirmed in North Dakota in Richland County in 2018. In 2020, it was confirmed in Cavalier County. There is probably more SDS in North Dakota then what we are aware of. The presence of SDS is closely linked to the presence of SCN. SDS shows up in fields in oval or circular spots or clusters of plants in a fields. The symptoms start as bright yellow spots that occur between the leaf veins that are not connected. As the disease progresses, the yellow spots turn brown and only the veins of the leaves stay green. To distinguish SDS from other diseases, look at the infected stems for tanning or browning but the center of the stems will remain white.
Charcoal rot is typically first noticed when patches of soybeans prematurely wilt and die. It is a disease that has caused severe yield loss in the southeastern part of the state and is probably more common in North Dakota than we think. The leaves will remain on the wilted and dying plants. Plant tissue on the lower stem and taproot may appear gray or silver. If you use a knife to remove the outer tissue on the lower stem of the plant, you will see charcoal-colored specs.
For more information about these late-season soybean diseases with good reference pictures, refer to the Soybean Disease Diagnostic Series (PP1867) publication that can viewed online. Or contact the Stutsman County Extension Office at 701-252-9030 or email Alicia at email@example.com.