Delayed planting, early frost, excessive rains, scorching drought, hail, wind, nutrient deficiencies, pests, weeds.

Pick your challenge to growing a high-yielding soybean crop. As a farmer, it’s your annual reality.

Did you know, however, that there is high probability that your yield losses are due to soybean cyst nematode?

Don’t think that’s an issue in some of your fields? You planted SCN-resistant varieties so you’re covered?

Got test results to support your belief?

If not, grab a bucket and shovel. Now. Dig up some plants and look for cysts on plant roots. Better yet, invest in soil SCN sampling.

According to University of Minnesota Extension crop scientists, SCN is widespread across the state. Soybean fields in more than 65 counties have been confirmed to have SCN, and the pest continues to spread. Experts say the microscopic roundworms that infect plant roots can cause yield loss up to 30%. The kicker? SCN can be present in a field for years before it is identified, and when you do see symptoms—stunting and yellowing, they look like symptoms caused by other pathogens or stressors.

Dorian Gatchell, agronomist and owner of Minnesota Agricultural Services, Granite Falls, Minn., believes that SCN has zapped soybean yields. He sees growers following extensive agronomic practices to attain higher yields, but often those efforts do not include SCN management. Plus, disease resistance in SCN-resistant varieties is failing.

“When a grower asks, ‘Why didn’t my soybeans do well?’ my first response always is ‘What is your SCN level?’” Gatchell says.

Sample and know

The best time to check for SCN is now, when cysts are visible on plant roots. This is only a simple visual check, however. It does not tell you the level of infestation. To learn that, you need a SCN soil test to identify nematodes and tell you the number of eggs per 100 cc in the soil.

Keep in mind that the test results are only accurate for the sampled site. Ideally, sampling will reflect the field and include low-yielding spots where SCN may be.

Gatchell knows that visualizing SCN distribution across a field is difficult. He has grid-sampled for nematodes, which is not cheap. Yet it is the best way to learn SCN status in a field.

To help pinpoint areas in the field to soil-sample for SCN, Gatchell uses a drone and NDVI (normalized difference vegetation index) imagery. With a multispectrum camera, he shoots images that show which plants are stressed.

“I’ve learned that this time of year, I can take an image and then direct where to take soil samples to identify SCN in the field,” he says.

Another way that Gatchell has been finding SCN in fields is collecting samples for soil DNA testing.

“The lab identifies sequences of DNA in the soil — not just for nematodes but for other pests, too,” he says. “It’s a cheap test to take. Then you can go back and take an egg count.” The soil DNA testing does take some time. He sends samples in the fall to a lab in California and gets results back in the spring.

Manage that yield hit

“If you don’t know if your fields have SCN, you can’t manage for them,” Gatchell says. He’d like to see growers be proactive in managing for the yield-robbing pest.

“Some fields have become unfit for soybean production because of SCN,” he says. “For those, the best agronomic advice for SCN management is don’t plant soybeans.”

That would mean going to a corn-on-corn rotation or adding any non-host crop, like small grains or alfalfa.

To settle for one-third yield reduction does not sit well with Gatchell.

“If you have varied yields and a spot in the field that consistently produces 60-plus bushels, you may be happy about that,” he says. “If that spot has high levels of SCN, then it probably should be doing 90-plus bushels. You shouldn't be happy about that.”

Learn more about SCN online at extension.umn.edu/soybean-cyst-nematode.