For two decades, soybean cyst nematode (SCN) management has been easy. Unfortunately, those days are coming to an end, says Iowa State University nematologist Greg Tylka.

“We’re kind of victims of our own success,” Tylka says. “We taught farmers to manage SCN with resistant varieties. Those varieties are quickly losing their effectiveness.”

More than 95 percent of SCN-resistant soybean varieties on the market today contain a single source of resistance — called PI 88788. Repeated use over the years has allowed SCN to overcome that resistance and reproduce on soybean varieties containing the PI 88788 breeding line, Tylka reports.

“It’s much like how the herbicide resistance problem...