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SCN Coalition Launches to Beat No. 1 Soybean Yield Robber

Research shows nematodes are becoming resistant to the resistance.

The No. 1 yield-robbing soybean pest for U.S. farmers has a new target on its back. Analysis of soybean variety trials conducted by Iowa State University (ISU) shows conclusively that soybean cyst nematode (SCN) is adapting and reproducing on the PI 88788 resistance source – used in more than 95% of resistant soybean varieties – and yields are decreasing.

Reversing this trend requires a comprehensive SCN management plan. The SCN Coalition has stepped in to fill those shoes after a 20-year hiatus.

“The nematode has found ways to overcome the resistance and become aggressive,” says George Bird, Michigan State University nematologist.

The coalition’s message is 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.

“Twenty years ago, most soybean growers had never tested their fields for SCN,” says Greg Tylka, nematologist at ISU 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.”

The previous coalition ended because it accomplished the mission of raising awareness. “We did a great job,” says Tylka. “We educated farmers about the threat. Then funding was shifted to the plant breeding.”

And over time, profitability of the breeding line PI 88788 beat out the rest of the resistant variety lines. But nematodes became resistant to the resistance.

SCN Reproduction

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, explains Bird. 

Data from 25 years of ISU 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 soybean plants showing visible symptoms.

SCN Yield

Coalition leaders believe Iowa is representative of what’s happening through most of the soybean-producing areas of the Midwest, where 70% of soybeans are grown. That’s why the SCN Coalition is back, warning growers about increasingly aggressive SCN populations and encouraging them to actively manage SCN.

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

  • Test your fields to know your numbers. “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.”
  • Rotate resistant varieties. While PI 88788 is the main source of resistance used today, other sources of resistance are available, explains Bird.
  • Rotate to nonhost crops. While a corn and soybean rotation is the most dominant rotation in the Midwest, if you can increase your rotation to three years of no soybeans, you’re going to decrease your SCN risk, says Bird.
  • Consider a seed treatment nematicide.

“It’s important for farmers to understand that they’re never going to get rid of soybean cyst nematode once they find it in their fields,” says Tylka. “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.”

By turning up the volume on SCN resistance management, the goal is to increase soybean farmers’ profit potential and realize higher yields. The coalition relaunched after 20 years thanks to a partnership of industry, says Bird.

SCN Varieties

Funding for the SCN Coalition came from North Central Soybean Research Program (NCSRP), the United Soybean Board, and in-kind support from coalition partners. Partners currently include university scientists from 27 states and Ontario; NCSRP, USB, and several state soybean promotion boards; corporate partners BASF, Bayer, Growmark, Monsanto, DuPont Pioneer, Syngenta, and Winfield United.

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