COLUMBIA, Mo. – Oct. 2 is National Nematode Day and marks a good time to test fields for soybean cyst nematode (SCN), the No. 1 pathogen of soybean in the United States.

“We anticipate the highest SCN levels to occur at the end of the season. Identifying problematic areas this fall can help with 2024 planting decisions,” said Mandy Bish, University of Missouri Extension plant pathologist and director of the SCN Diagnostics clinic.

The clinic has partnered with the Missouri Soybean Merchandising Council to provide Missouri farmers four free SCN egg count tests this fall.

Soybean infected with SCN often appear healthy above the ground because SCN infects the roots of plants. “However, the severe drought during the 2023 season may have unmasked some of our problematic areas,” said Bish. “We have patches of yellow soybean appearing in many fields this year, and there are multiple causes. One contributing factor in some fields may be high SCN levels. A soil test will help determine whether SCN pressure is adding to the problem.”

To determine if SCN is present, collect soil samples in fields:

• Sampled more than three to five years ago.

• With known SCN populations.

• With a history of sudden death syndrome of soybean.

• Where soybeans are not rotated with corn.

Sampling for SCN is a little different than sampling for other purposes, said Bish. Recommended soil cores are 1 inch in diameter by 8 inches deep.

For more than three decades, growers have relied on a soybean line called PI 88788 as the main defense against SCN. More than 95% of commercial varieties grown in Missouri have PI 88788 resistance. Juvenile nematodes feed on roots of PI 88788 plants, which impedes their maturation into adult females, stopping egg production. But recent work by MU soybean researchers found that some juvenile nematodes can feed on PI 88788 soybean and still mature into adult females.

“Thirty years is a long time to rely on one management tactic,” said Bish.

The SCN Coalition recommends four ways to manage SCN:

• Test fields to “know your numbers.”

• Rotate resistant varieties.

• Rotate to nonhost crops.

• Consider using a nematode-protectant seed treatment.

“Sampling can be frustrating because nematodes do not appear uniformly in fields,” Bish said.

The SCN Coalition makes these recommendations for sampling:

• Divide fields into sections of 10-20 acres using natural boundaries such as different topographies, areas where sudden death syndrome or SCN symptoms appeared previously, and low-yielding areas of the field.

• Collect 15-20 soil cores from each section of the field. Collect in a zigzag pattern. Dig cores 1 inch in diameter and 8 inches deep. Mix the cores together within sections and put in sample bags.

• Submit samples for each section separately to SCN Diagnostics.

Download the sample submission form at https://scndiagnostics.com/links/sample_submission_form.pdf. For more detailed sampling instructions, go to http://bit.ly/3B4PcrY (PDF).

For more information, contact the clinic at scndiagnostics@missouri.edu.

SCN Diagnostics is a partnership with the University of Missouri and MU’s College of Agriculture, Food and Natural Resources.

Bish and other MU researchers continue to study how in-season management practices influence SCN levels. Learn more at ipm.missouri.edu/cropPest/2022/9/scn-MB.

Photos:

https://extension.missouri.edu/media/wysiwyg/Extensiondata/NewsAdmin/Photos/2023/20230921-scn-1.jpg
SCN females on soybean plant. Photo courtesy MU senior research specialist Jeff Barizon.

https://extension.missouri.edu/media/wysiwyg/Extensiondata/NewsAdmin/Photos/2023/20230921-scn-2.jpg
MU undergraduate Sam East sampling a Missouri soybean field. MU Extension photo.