Iowa State University nematologist Greg Tylka says soybeans with Soybean Cyst Nematode resistance are becoming less effective. He calls it an alarming trend that sets the stage for even more yield loss to SCN in the future. Farmers have effectively managed the pest for decades thanks to the built-in resistance.
Just about all the SCN-resistant varieties have the same resistance gene. Iowa State researchers analyzed 25 years of data from four-row variety evaluation research plots to look for long term trends. The results show a breakdown in resistance in SCN-resistant soybeans.
“In the 1990s, SCN was well controlled by the resistance gene,” says Tylka. “Starting in 2001, we saw a steady decrease in control of SCN in the varieties that had the resistance gene.” He says the buildup in SCN resistance is similar to weeds developing resistance to glyphosate after prolonged use of a single mode of action. The study concludes that resistance issues will worsen if farmers only have the same resistance gene going forward. Tylka adds, “This is a serious situation. SCN has infested 70 percent of Iowa’s soybean fields.”