Soybean Cyst Nematode Spread Continues
SCN Expands in US and Canada, Threatening Soybean Yields
DECATUR, Ill. (DTN) -- Soybean cyst nematode (SCN) has been stealing yields since 1954, often without any obvious aboveground signs that it's grabbing a free lunch. A new study shows it continues to increase its appetite for dining in new locations.
Organized efforts to document SCN distribution have been tracking the spread since 2000. The latest survey effort to bring the map up to date adds 31 counties in 10 U.S. states reporting SCN for the first time during the 2020-2023 timeframe. In Canada, 10 rural municipalities in Quebec and three counties across Manitoba and Ontario reported SCN for the first time over that three-year span.
Beginning in January 2024, university nematologists, plant pathologists, agronomists and government plant health officials in soybean-producing states in the United States and provinces in Canada were queried about the known distribution of the nematode. The effort was spearheaded by Iowa State University nematologist Greg Tylka, and the entire report can be viewed here: https://apsjournals.apsnet.org/… .
Most of these newly identified infestations (see blue on map) lie on the fringe of an already existing sea of red on the SCN distribution map. For example, SCN has already been found in every county in Illinois and Iowa, the top two soybean-producing areas.
Just because an area is not reporting SCN does not mean fields there are free of the pathogen. "Fields may be infested with the nematode for many years before infestations are discovered," according to the report.
Researchers have established that SCN costs U.S. soybean farmers more yield than any other pathogen. Losses due to SCN are double those of the next largest pathogenic threat. Based on SCN's ongoing spread, Tylka observed: "It's reasonable to conclude that increased soybean yield losses due to the nematode will follow, if they are not already occurring in these areas."
SHAKE UP RESISTANCE
Soybean varieties with genetic resistance to SCN have saved countless bushels over the years. However, decades of reliance on the most popular source of resistance, PI 88788, have resulted in SCN populations resistant to the resistance.
The good news is new sources of resistance, such as Peking, are being offered more frequently. "Farmers now have many choices of varieties with Peking SCN resistance from many brands," Tylka said. "That enhances their ability to rotate resistant varieties, a key element of active SCN management."
To combat mounting resistance to PI 88788, The SCN Coalition encourages farmers to work with their trusted agronomic adviser to develop a plan, including:
-- Test fields to know your numbers.
-- Rotate resistant varieties.
-- Rotate to non-host crops.
-- Consider using a nematode-protectant seed treatment.
Because soybeans with Peking SCN resistance will likely outyield PI 88788 resistance varieties in SCN-infested fields, it can be tempting to plant Peking over and over, Tylka noted. However, prolonged use of Peking SCN resistance will create its own resistance battle. The best strategy is to rotate resistance types. Soybean seed providers should provide information on the type of resistance within each variety.
According to Iowa State University's annual check-off funded publication, the number of varieties with Peking resistance available to Iowa farmers in 2025 more than doubled from last year to 200. You can download the complete list of the 920 SCN-resistant soybean varieties available in that state here: https://store.extension.iastate.edu/…
Worried that SCN is lurking and wonder how much it is costing you? The SCN Profit Checker puts dollars and cents on the toll. The free calculator uses data from more than 25,000 university research plots and is available here: https://www.thescncoalition.com/…
To learn more about active SCN management in your state, visit thescncoalition.com/experts.
In 2024, DTN partnered with The SCN Coalition to dig deeper into SCN. Read more about HG type testing here: https://www.dtnpf.com/…
Learn basic facts about SCN and how it infests fields here: https://www.dtnpf.com/…
Consider these five steps when SCN threatens to reduce yields: https://www.dtnpf.com/…
To learn more about active SCN management in your state, visit thescncoalition.com/experts.
Pamela Smith can be reached at pamela.smith@dtn.com
Follow her on social media platform X @PamSmithDTN
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