Crops News

SCN Coalition is back in fight against soybean cyst nematodes


After a 20-year hiatus, the SCN Coalition is back encouraging soybean farmers to “Take the test. Beat the pest.” Like the predecessor, the new SCN Coalition is a public/checkoff/private partnership formed to help the agricultural industry speak with one voice about soybean cyst nematode management.

The difference this time: SCN is adapting and reproducing on SCN-resistant soybean varieties – and yields are decreasing. Managing SCN is becoming more complicated than planting a resistant variety and assuming the problem is solved.

“Twenty years ago, most soybean growers had never tested their fields for SCN,” says Greg Tylka, Ph.D., nematologist at Iowa State University and veteran of the first SCN Coalition. “So we encouraged growers to test, and if they had it, to plant a variety that’s resistant to SCN.”

That simple solution from 20 years ago is becoming a problem today because greater than 95 percent of all SCN-resistant soybean varieties contain the same source of resistance from the PI 88788 breeding line.

“It’s much like how the herbicide resistance problem developed,” Tylka adds. “After two decades of using the same source of SCN resistance, we’re seeing natural selection in action. The nematodes are adapting.”

A resistant soybean variety should allow less than 10 percent reproduction versus a susceptible variety. In other words, a resistant variety should stop 90 percent of the SCN in a field from reproducing. Currently, researchers are discovering that on some farms, one out of every two nematodes can reproduce on a variety with PI 88788 resistance (that’s 50 percent reproduction).

Data from 25 years of Iowa State University variety trial experiments shows that as SCN reproduction increases on PI 88788, yields of resistant soybean varieties decrease by as much as 14 bushels per acre. “One of the problems is that SCN can cause yield loss without the plants and the crops looking sick,” Tylka says.

Coalition leaders believe Iowa is representative of what’s happening through most of the soybean-producing areas of the Midwest, where 70 percent of soybeans are grown. And according to Tylka, “Other states might be farther along in this problem than we are.”

That’s why the SCN Coalition is back, sounding the alarm over increasingly aggressive SCN populations and encouraging growers to actively manage SCN. That starts by testing your fields for SCN so you know what your populations are doing.

“You’ll need those numbers to understand the severity of the problem,” Tylka continues. “The higher your numbers, the greater your chances of yield loss, and the higher that yield loss will likely be.

“It’s important for farmers to understand that they’re never going to get rid of soybean cyst nematode once they find it’s in their fields. But it’s not a death sentence. It’s similar to finding out you have high blood pressure – you learn to manage it as a chronic health problem,” he says.

Because each grower’s SCN numbers, situation, and available management options will be unique, the SCN Coalition recommends that soybean farmers work with their advisors and develop a plan to actively manage SCN:

  • Test your fields to know your numbers.
  • Rotate resistant varieties.
  • Rotate to non-host crops.
  • Consider a seed treatment nematicide.

By turning up the volume on SCN resistance management, the Coalition’s goal is to increase soybean farmers’ profit potential and realize higher yields. The Coalition relaunched after 20 years, thanks to funding from the North Central Soybean Research Program (NCSRP), the United Soybean Board (USB), and in-kind support from Coalition partners.

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