Know your SCN numbers?

Photo by Kaitlyn Bissonnette

Coalition recommends testing soil after harvest to find out

Now is the time to test fields for soybean SCNnumberNematodesPhotobyKaitlynBissonnettecyst nematode (SCN), the most economically damaging pathogen for soybeans in North America. Right after soybean harvest is when SCN egg counts will be highest, according to Mandy Bish, University of Missouri Extension specialist and interim director of the SCN Diagnostics clinic.
SCN appears in the roots of plants, and symptoms are often difficult to see with the naked eye, so infected fields may look healthy above ground. A soil sample will help determine its presence and level of infection.

The parasitic roundworm, which feeds on the roots of soybeans and other legumes, was first detected in the United States in 1954. Today, the pest causes more than $1.5 billion in damage annually, according to the SCN Coalition, a group of public universities, checkoff organizations and corporate partners working to raise awareness and combat the pest.

Bish said SCN is present in approximately 85% of Missouri fields, and there can be six generations per growing season. Even without evidence of symptoms, SCN can cause yield losses of up to 30%. And SCN can survive under adverse conditions, including the hot, dry weather experienced across MFA territory this past growing season.

Another concern, she added, is that SCN is adapting to resistant soybean varieties. For more than three decades, growers have relied on a soybean breeding line called PI 88788 as the main defense against SCN. Juvenile nematodes feed on roots of PI 88788 plants, which impede their maturation into adult female SCN, stopping egg production. But recent work by MU soybean research teams found that some juvenile nematodes can feed on PI 88788 soybean and still mature into adult females.

Among tactics are:
• Testing your fields to know your numbers
• Rotating to non-host crops
• Rotating resistance sources
• Rotating varieties with the same resistance
• Using nematode-protectant seed treatments
• Managing weedy hosts
• Maintaining plant health

“Thirty years is a long time to rely on one management tactic,” Bish said.
Managing for SCN takes a multi-faceted approach, she added. If SCN is determined
to be a problem in your fields, MFA agronomists can help growers with a plan for 2023.
Among tactics are:

Soybean growers who haven’t tested for SCN in recent years are encouraged to assess the pathogen’s presence in their fields this fall. Farmers can receive two free SCN egg count tests, a service provided by SCN Diagnostics, United Soybean Board, Missouri Soybean Merchandising Council and the SCN Coalition. Additional samples will be $25 each. The sample submission form is available online at scndiagnostics.com. Fields that have been in continuous soybean production or are prone to sudden death syndrome are good places to start.

For more information on SCN and to find detailed sampling instructions, visit thescncoalition.com.

Image caption: Soybean cyst nematode is a microscopic roundworm that attacks roots of soybean and a number of other host plants. The nematode can be present in fields without causing obvious above-ground symptoms. Producers are encouraged to test fields for SCN after soybean harvest. Photo by Photo by Kaitlyn Bissonnette.

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