Until recently, the threat from soybean cyst nematodes (SCN) seemed a thing of the past. Thanks to soybean varieties largely derived from the SCN-resistant PI88788 or Peking lines, growers could plant in complete confidence that SCN would not reduce their high yields. Over the past 20 years or so, however, the pathogen has gradually built up its own resistance to these soybean varieties, allowing it to multiply in fields that were previously unaffected.

Anne Dorrance, a plant pathologist at The Ohio State University, understands the gravity of the situation. “This pest is a yield robber. It’s not a killer,” Dorrance says. She further notes that farmers can’t always quickly diagnose the problem because some SCN infestations produce very few visible symptoms.

That’s why Dorrance is leading Ohio’s efforts in the SCN Coalition, a multistate, checkoff-funded collaboration of researchers striving to increase awareness about SCN and develop effective solutions for soybean growers. The SCN Coalition’s slogan is “Take the test. Beat the pest!” meaning farmers should test their soils even if they don’t think they have a problem. Over the next year or so, Dorrance will have tested several thousand soil samples from soybean growers all across Ohio.

A recently completed study revealed that about 90 percent of tested samples were below the 2,000 eggs/cup soil economic threshold for SCN-related yield loss. However, those samples were taken from high yielding fields. Dorrance feels this may not be giving growers an accurate picture for their whole farm.

“I want your lowest yielding spot that you know is not from flooding or something else like that,” she says. Dorrance expects this sampling method will show only 75 percent of tested samples are under the economic threshold, especially since she has already documented several SCN hotspots across the state with levels up to 30,000 eggs/ cup soil.

Even though resources for combating SCN are limited, Dorrance believes the Coalition will streamline efforts to help farmers now and into the future. In the short term, researchers are evaluating combinations of biological and/or chemical seed treatments with the failing, formerly resistant soybean lines to increase options for farmers. Over the long term, however, researchers are focused on generating new soybean lines with more genetic diversity to allow them to better withstand SCN pressure.

With these efforts, combined with farm-specific solutions from Dorrance and other specialists, growers should already see the light at the end of the tunnel for overcoming SCN and enjoying higher soybean yields once again.

 

Soybean Cyst Nematode Quick Facts

  • SCN has three general life stages: egg, juvenile and adult. In Ohio, the SCN lifecycle takes about three to four weeks, so soybean fields can experience several generations in a single season.
  • Cysts are formed when the female nematode dies, leaving a strong protective coating around the egg mass.
  • Encased in cysts, SCN eggs can hatch over a long period of time, even years.
  • Once hatched, juvenile nematodes feed on the soybean roots.
  • This pest is largely spread mechanically by farm equipment or naturally by wind-or water-borne soil.
  • The economic threshold for SCN-dependent yield loss is 2,000 eggs per cup of soil.
  • Once present in the soil, SCN is rarely eradicated. Crop rotation to non-host plants like corn and wheat can reduce SCN populations, as well as seed treatments and biological controls.
  • Over the past 20 years, the pest has slowly adapted to the once very effective SCN resistant soybean varieties. Current research aims to generate new resistant soybeans by including more genetic diversity to greatly reduce the likelihood that SCN populations will survive over the long term.
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