Soybean Cyst Nematode (SCN)

Soybean cyst nematode (SCN) in the United States was first observed in 1954 in North Carolina, and it has continued to spread throughout most of the major soybean growing areas (Tylka and Marett 2014). The expansion of SCN across the U.S. and Canada is depicted in Figure 1. It is the most damaging pest in soybeans by a large margin. Soil sampling for SCN presence is fundamental to understanding local, field-level presence.

Left: Average soybean yield loss (in millions of bushels) each year from the top five diseases in the United States and Ontario, Canada. Source: Allen et al., 2017.
Right: The percentage of SCN populations in a state/province with elevated reproduction (>10%) on PI 88788. In most Midwestern states, soybean cyst nematode is resistant to varieties with PI 88788, the most common source of SCN resistance on the market. Peking varieties could help farmers, but they remain a tiny fraction of the soybean market. (Photo courtesy The SCN Coalition)

Soon after SCN was discovered in the U.S., SCN-resistant germplasm sources were identified and developed. Over the years, they have increasingly been incorporated into soybean breeding programs across the industry. By the 1990s, most soybean variety releases contained a genetic source for SCN resistance. Industry-wide, over 90% of all new soybean varieties include SCN resistance.

There are multiple sources of genetic SCN resistance, but PI88788 source of resistance is widely adopted. Because of the almost exclusive reliance on this single source of genetic resistance, SCN populations have evolved to reproduce on varieties, including the PI88788 source of resistance (Figure 2).

Peking is another popular, commercially available source of genetic resistance that remains effective in PI88788-tolerant populations. Universities and the seed industry continue to work with alternative genetic resistance traits, but other commercial options are very limited today.

In many fields across the U.S., SCN is present, yet the symptoms are subtle or not visible at all. In areas within fields with larger populations, the symptoms can include yellowing and stunting of the soybean plants. However, significant yield impact from SCN can happen in the absence of visual above-ground symptoms. In addition to direct yield loss, SCN damage can lead to earlier development and increased incidence of critical soil-borne diseases like sudden death syndrome and brown stem rot.

1. Soil Sample

The magnitude of possible soybean yield losses corresponding to SCN soil sample egg count results from the Iowa State University Plant and Insect Diagnostic Clinic. Source: Iowa State University

2. Evaluate Soybean Fields

Check for evidence of yellowing or stunting from SCN during the growing season.

3. Dig Plants

During the summer, dig soybean plants to see if there is evidence of cysts on the roots.

Once SCN is present in a field, it’s nearly impossible to eradicate the pest. It is critical to avoid moving the pest from infected areas to unaffected fields. Cleaning equipment before entering fields with no known SCN pressure is an important step.

1. Rotate to non-host crops and keep weed pressure low, especially weeds that are SCN hosts. If fields have severe SCN populations that make soybeans not economically viable, use multiple years of non-host crops before growing soybeans again (Figure 2).

2. Plant varieties with genetic resistance to SCN; try to incorporate soybean varieties that have the Peking source of SCN resistance.

3. Use seed treatments that contain nematode control. There are several different seed treatment products on the market with activity on SCN that can be incorporated into an integrated approach to combat this pest.

Seed treatments for SCN should focus on early-season protection as these products are protecting the young seedlings from the first hatch of SCN. One line of defense is with Escalate® | Nemasect® | SDS+, which comes standard on all Beck’s soybeans or try Beck's upgraded Escalate | Nemasect | SDS+ | ILEVO® TWO.O® option for an additional layer of protection from the ILEVO. This treatment includes two modes of action against SCN and provides plants with the best possible start Beck’s can offer.

Soybean cyst nematodes have spread and now encompass much of the soybean growing area, making it extremely important to take soil tests to understand SCN egg counts. If SCN populations are present in a field, the incorporation of management practices to reduce SCN populations are critical to maintaining soybean productivity.

Learn more about SCN management at Take the test. Beat the Pest (thescncoalition.com).

Allen, T. W., et. al (2017). Soybean Yield Loss Estimates Due to Disease in the United States and Ontario, Canada, from 2010 to 2014. Plant Health Progress. 2017, 18, 19-27.

Tylka and Marett, 2014. “Distribution of the Soybean Cyst Nematode, Heterodera glycines, in the United States and Canada: 1954 to 2014.” Plant Health Progress 15(2):85-87. https://www.plantpath.iastate.edu/scn/management-scn

Wrather and Mitchum, Revised August 2010. “G4450 Soybean Cyst Nematode: Diagnosis and Management.” University of Missouri Extension. Retrieved March 23,2020 http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.aspx?P=G4450.