Specialist Identifies Soybean Cyst Nematode in Three Additional South Dakota Counties

Soybean cyst nematodes are in every South Dakota county east of the Missouri River, as well as a couple of West River counties. Three counties where SCN has been newly detected are Faulk County, east of the river, and Jones and Lyman Counties, west of the river, according to Dr. Madalyn Shires, plant pathology specialist at the South Dakota State University Extension Service.

“We were doing random soil surveys around soybean growing fields and could find nematodes roughly about 95 percent of the time,” Dr. Shires told the South Dakota Soybean Network. “So, they're quite widespread, and unfortunately, they're kind of that silent yield robber; they're not always recognized if the field has not been tested.”

Early stages of SCN infestations are often undetected until fields are tested. Now is a good to do that.

“This is actually the best time of year to test,” explained Dr. Shires. “We're able to kind of see the results of those two to three generations of nematodes and be able to have a very accurate estimation of what your SCN number is in your field.”

Without testing, fields appear to be normal, but yields are being reduced resulting from the parasitic roundworms reproducing and feeding on soybean roots.

“That feeding behavior and reproduction actually end up causing damage to the roots and reducing the way that those roots are able to take up water and nutrients and feed the plant,” she said.

The most common and simple tests conducted at the SDSU laboratory count SCN eggs and cysts and cost $50 per sample. A sample is 20 soil cores collected in a zig-zag pattern in a field.

As part of her master’s degree work, graduate student Nabina Karki performed the more sophisticated HG – Heterodera glycines – testing in 40 South Dakota counties. HG testing determines the effectiveness of the SCN resistance gene PI 88788, which was developed years ago to combat the pest but packs less punch than it once did.

“Eighty-five percent of those populations were partially or fully resistant to PI 88788,” said Dr. Shires, “which means that they were able to effectively feed and reproduce and have multiple generations of nematodes each year on previously resistant genes. And [Ms. Karki] is also finding that with the Peking gene too, but its resistance is lower, I believe between 35 and 45 percent.”

The Peking gene remains an alternative for growers when SCN populations have become tolerant of the PI 88788 gene.