DECATUR, Ill. (DTN) -- Rotating soybean cyst nematode (SCN) genetic resistance is a strategic management move. But it requires being proactive during seed selection to learn the source of SCN resistance within each variety, according to Greg Tylka, Iowa State University nematologist.

The industry has long relied on PI88788 resistance to deal with SCN, the leading yield-robbing pathogen of U.S. soybeans each year. When nematodes started defeating this resistance, soybean breeders went to work to develop varieties containing an alternate resistance called Peking.

Still, PI88788 varieties continue to dominate seed catalogs, and the source of resistance isn't always apparent or consistently communicated, Tylka noted in a recent blog post. That information is especially important when selecting for alternatives and to allow rotation between resistance offerings.

To help Iowa farmers know what options are available, Tylka leads field experiments each year to test the yield and SCN control of resistant varieties around the state. Farmers in other states who plant soybeans of similar relative maturities can also use these listings to glean clues. The results of the testing are made possible by checkoff funding through the Iowa Soybean Association.

For the 2026 growing season, Tylka found Iowa farmers can choose from 908 SCN-resistant varieties, from 35 brands and 25 seed companies. Varieties in roughly 78% of this year's list contain PI 88788 resistance, nearly 22% use Peking resistance, and a handful of varieties use a blend or physical mixture of two varieties with the two resistance modes.

Find the entire listing of SCN varieties here: https://www.thescncoalition.com/… and Tylka's blog post here: https://www.thescncoalition.com/….

ROTATE RESISTANCE

SCN's increasing reproduction levels on PI 88788 may tempt some farmers to plant soybeans with more effective and often higher-yielding Peking resistance year after year, but Tylka warns against it.

Exclusive use of Peking resistance could lead to even more SCN reproduction and fewer options for managing the parasitic nematode, he said.

"Peking is fast-acting and highly effective, so very few nematodes are able to overcome Peking resistance," Tylka explained. "But those that do reproduce on plants with Peking resistance are likely to pass that ability on to their offspring."

Read more about the lessons of overusing one type of resistance here: https://www.thescncoalition.com/….

DEVELOP SCN STRATEGY

The current input cost/commodity price squeeze increases the emphasis on finding ways to reclaim yield. Nematodes thrive on droughty conditions and that adds motivation to form a strategy to manage the pest.

Tylka and The SCN Coalition recommend farmers include these steps as part of their active management program.

-- Start growing varieties with Peking SCN resistance NOW.

-- Never grow varieties with Peking SCN resistance in consecutive soybean crops.

-- Alternate growing Peking SCN-resistant varieties with varieties containing PI 88788 resistance.

-- Plant non-host crops, such as corn, in annual rotation with soybeans.

There's no silver bullet for wiping out SCN (yet), but Tylka said strategically rotating resistance and non-host crops such as corn can slow or possibly prevent populations of SCN from becoming resistant to the two modes of resistance. Learn more about SCN management at TheSCNCoalition.com.

For a recent DTN article on dry weather and SCN go to: https://www.dtnpf.com/….

Find a video on how to soil test for SCN here: https://www.youtube.com/….

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social media platform X @PamSmithDTN

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