Soybean cyst nematode (SCN) continues to adapt to PI 88788, the most common source of SCN resistance in soybean varieties, according to a new analysis of more than two decades of Iowa State University research.
Researchers analyzed data from SCN-resistant soybean variety trials conducted across Iowa from 2001 through 2023. The study, recently published in Plant Health Progress, was funded by soybean checkoff dollars through the Iowa Soybean Association.
The results show that SCN populations continue to reproduce more successfully on PI 88788-resistant soybeans. Reproduction on PI 88788 increased about 2% per year during the 23-year period.
The findings are consistent with predictions Iowa State nematologist Greg Tylka and other researchers made nearly a decade ago.
“It’s interesting that predictions we made nearly a decade ago proved remarkably accurate,” says Tylka, a co-author of the study, in a press release. “SCN populations continue to adapt to PI 88788 resistance, and if we don’t diversify how we manage the pest, farmers can expect that trend to continue.”
What Could This Mean For Yields?
Researchers estimate that by the end of this decade, PI 88788 resistance could provide only about 40% control of SCN if current management practices remain unchanged.
That could translate to average yield losses of about 9 bushels per acre, or roughly 12% of yield potential.
By comparison, effective SCN resistance typically provides 90% or more control of the pest.
The findings reinforce a message farmers have heard for years: SCN management cannot rely on the same resistance source year after year.
Peking Resistance Needs Monitoring, Too
Peking is currently the other major SCN resistance source used in soybean varieties available to Iowa farmers.
Researchers did not find a significant statewide increase in SCN reproduction on Peking resistance during the study period. However, they did find more individual trial fields with elevated reproduction on Peking from 2016 through 2023 than during the previous 15 years.
That makes continued monitoring important as more Peking varieties become available.
The HG type test can help determine how well an SCN population is controlled by Peking, PI 88788 and five other resistance sources that are not currently available in commercial soybean varieties.
“We cannot afford to repeat the mistakes made with PI 88788,” Tylka says. “Another wholesale shift to a single resistance source, like Peking, is likely to accelerate adaptation by SCN populations. The goal is long-term management that preserves the effectiveness of all available resistance sources.”
Diversify SCN Management
More soybean varieties with Peking resistance are becoming available, giving farmers another tool for managing SCN.
Researchers recommend using a mix of resistance sources rather than relying exclusively on PI 88788 or Peking. Farmers also can incorporate other SCN management practices, including nematode-protectant seed treatments and rotating with nonhost crops when appropriate.
Using both PI 88788 and Peking resistance in a balanced rotation could help slow SCN adaptation while maintaining soybean yield potential and reducing SCN populations over time.
“Soybean cyst nematode remains the most damaging soybean pathogen in North America, and it’s not going away,” Tylka says. “The good news is that farmers still have effective tools available today. By diversifying resistance sources and avoiding overreliance on any one strategy, farmers can reduce risk and help protect soybean yields for years to come.”
Although the study was conducted in Iowa, researchers say the issue extends beyond the state. Published surveys and observations from other Midwestern states indicate that increasing SCN virulence to PI 88788 is a regional concern.
Start With A Soil Test
Farmers can use soil testing to determine whether SCN is present and monitor population levels.
The SCN Coalition recommends sampling fields for SCN after harvest and entering test results into its SCN Profit Checker. The tool can help farmers estimate potential yield loss and profit risk associated with SCN.
For more information on SCN testing and management, visit The SCN Coalition.
