What is your next move if soybean yields didn’t meet expectations? Steve Gauck, a regional agronomy manager for Beck’s based near Greensburg, Ind., believes in asking questions. He monitored progress of the Soybean Watch ’24 field in south-central Indiana. Sponsored by Beck’s, this project provides real-life insights that could help growers unlock higher yields.

Yield fell short of what Gauck expected, especially in the toughest part of the field, a wide-sweeping, eroded hillside. “We needed to see what else might be in play,” Gauck says. “One thing to check is for soybean cyst nematodes. They can cause yield loss even when plants don’t show symptoms.”

Sure enough, SCN eggs were discovered. Counts in four sampling areas ranged from 300 eggs per 100 cubic centimeters of soil where yields were highest to 5,200 eggs per 100 cc where yields were lowest.

What comes next?

Once SCN was confirmed, two specialists answered questions about what the grower should consider doing next. Mandy Bish is an Extension plant pathologist at the University of Missouri, where the samples were analyzed for SCN, and Darcy Telenko is an Extension plant pathologist at Purdue.

What should the grower do first?

Bish: Rotate to corn for 2025. Then, consider planting a Peking soybean variety in that field for 2026.

Related:Hunch pays off: Testing finds SCN

Telenko: Here are the “big four” management steps. First, test the field — that is done. Nematodes were found at moderate levels. Next, rotate the type of resistant varieties, rotate to nonhost crops like corn, and consider seed treatment. Find helpful information at thescncoalition.com.

Why is it important to know SCN egg numbers, even if you have used SCN-resistant varieties before?

Telenko: The SCN Coalition offers this well-worded answer: “Managing SCN involves more than just planting an SCN-resistant variety. You need to know your numbers. Nearly all SCN-resistant varieties have the same source of resistance — PI 88788. SCN populations are adapting and reproducing on PI 88788. They’re becoming resistant to the resistance. As SCN reproduction increases, yield decreases.”

Editor’s note: About 95% of current soybean varieties with SCN resistance use PI 88788. The other 5% use Peking-type resistance. That’s why Bish suggests considering including it in your rotation if you can find a suitable variety. Currently, far fewer varieties with Peking resistance are available.

Why does crop rotation help?

Bish: When a nonhost crop is planted, SCN can’t reproduce during that season, which helps reduce overall population density in the field. Since SCN eggs can remain viable for more than one year, additional management strategies are needed alongside crop rotation to effectively manage nematode populations.

Related:What soil types are in your field?

If you can include both PI 88788 soybeans and Peking soybeans in the years you raise soybeans, instead of just one type of resistance, you buy yourself more time with each of those sources. Resistance should build up slower than if you always use the same type of resistance.

What type of resistance should growers look for?

Bish: As noted, PI 88788 resistance is most common and remains the primary source of SCN resistance. Rotating between Peking and PI 88788 is ideal, because they are genetically distinct. Including both types in the rotation along with nonhost crops can slow SCN’s ability to overcome other types of resistance. More recently, there have been increased efforts to develop commercial varieties with Peking resistance.

For Peking right now, there is one type of resistance available commercially. It includes two genes. However, scientists just discovered a third gene which can enhance resistance. So, in the future, there may be Peking-type resistance with two SCN-resistant genes and Peking-type resistance with three SCN-resistance genes. However, it is not yet available.

Are all PI 88788 varieties equal in terms of SCN resistance?

Bish: No. These PI 88788 varieties can differ in the amount of the SCN-resistant trait they possess. Varieties with more resistant DNA may correspond to higher levels of SCN protection. However, there is not a good way to know how much SCN-resistant DNA is present within a PI 88788 variety in advance. Rotating between different PI 88788 varieties may help, but it is still better to rotate between Peking-resistant and PI 88788-resistant varieties.

Should additional testing be done to determine the specific type of genetic resistance to seek?

Telenko: This would be where you could consider HG testing. It is much more expensive than just asking the lab to analyze soil samples for cyst nematode eggs.

Bish: For most cases, SCN management recommendations will be the same regardless of results from HG testing. I suggest farmers focus on SCN egg counts, which are quicker and less costly compared to HG tests.

The Heterodera glycines test measures how well the SCN population can reproduce on different soybean lines. It compares SCN reproduction on susceptible soybeans to varieties with various types of resistance. High SCN egg counts at harvest can be an indicator that your soybean variety, whether PI 88788 or Peking, is not working optimally with regard to managing SCN. An HG-type test can confirm it.

However, we will always recommend rotating with a nonhost crop and rotating between soybeans with PI 88788 and Peking resistances, regardless of HG results.

Will seed treatments help?

Bish: Seed treatments may help, but they can be dependent on environmental conditions and SCN population densities. They must be accompanied by additional management strategies.

Once you know you have SCN, how should you monitor it going forward?

Bish: The best way to monitor SCN and assess effectiveness of your management strategy is to test for SCN egg counts both at planting and at harvest. Did population densities increase, decrease or remain the same throughout the season?