Do not confuse soybean cysts with soybean nodules—the three cysts above are much smaller.
If you don’t know whether soybean cyst nematode (SCN) lurks in your fields, this spring would be a good time to figure that out. This microscopic roundworm with a voracious appetite robs farmers of more than $1 billion each year. The high level of annual loss means SCN has the dubious honor of being the most serious soybean pathogen in North America.
To date, SCN has been identified as a significant pest in 31 states and Canada. Yield losses in an infected soybean field commonly top 30%, according to plant pathology scientists at the University of Minnesota (UM).
Their research shows that SCN stunts soybean root growth, impairs root translocation of water and nutrients, strips nutrients from soybean plants, reduces nitrogen fixation and makes soybean roots more susceptible to soil-borne plant pathogens.
A view through the microscope shows a cyst that broke open releasing eggs and juvenile nematodes. Photo by Amanda Anderson
Furthermore, SCN is commonly associated with the development and spread of the fungal disease, Sudden Death Syndrome (SDS), notes Missy Bauer, Farm Journal Associate Field Agronomist. University research shows SCN hastens the development of SDS symptoms and increases their severity, leading to greater yield loss.
The presence of SCN in fields is often ignored or misdiagnosed, as its above-ground symptoms are similar to other issues such as nutrient deficiency, drought stress, herbicide injury and disease. In addition, once established in a field, SCN is rarely eradicated, and its eggs can survive in the soil for many years.
SCN moves about very little under its own steam, but infested soil is readily spread by heavy rains and snowmelt. Flood-prone areas, river bottoms, field entrances and sections along fence lines often have high concentrations of SCN-infested plants.
"Moving tillage equipment from one field to the next is another common way SCN is spread," Bauer says.
What to look for. In-season, there are certain signs of SCN to watch for in your crop. Starting about four to six weeks after crop emergence and continuing through late season, Bauer says to look for odd-shaped areas in soybean fields that appear to have been affected by drought or standing water. Bauer uses Normalized Difference Vegetation Index (NDVI) aerial image technology to identify the hot spots and then goes to the field to ground-truth the NDVI map.
"You need an NDVI with a 1-meter or less resolution for affected areas to show up well enough for you to see them," she explains.
Bauer advises farmers to dig up samples of soybean plants along the edges of the areas in question. Do not pull up the plants, as the SCN can be easily dislodged from the plant roots.
- Mid-February 2014