Managing the silent yield robber

October 30, 2025 | Kriss Nelson

Maybe you’re satisfied with this year’s soybean yields, or perhaps you’re wondering what more could have been done to bump those yields higher? If the latter is the case, one hidden factor could be soybean cyst nematode (SCN), a pest often called the silent yield robber.

Iowa Soybean Association (ISA) Research Agronomist Lucas De Bruin knows firsthand how damaging SCN can be and the importance of being proactive.

“You definitely want to keep an eye on it and be aware of it,” says De Bruin, who also farms near Oskaloosa. “I’ve seen SCN reduce soybean yields by more than 50 percent, even 70 percent. Sometimes it’s just bare spots in the field, and that really adds up. Take soil samples, look at your variety and pay attention to crop rotation. That’s the most important thing. Make a plan for next year.”

Soil test for results

Getting ready for the 2026 growing season starts with knowing your enemy. Soil sampling is the first step in managing SCN before it robs next year’s yield.

“Most importantly, farmers should start by assessing their situation, beginning with soil sample results, especially in fields that will be planted with soybeans next year,” said Greg Tylka, Morrill Professor and nematologist at Iowa State University.

 Tylka says there are two approaches to soil sampling for SCN.“The first one that may come to a farmer’s mind is sampling harvested soybean fields, and that approach is fine. The results will provide a look back at what could have happened during the season,” says Tylka. “If yields were 42 bushels per acre and expectation was 55, and they found a few thousand SCN eggs per half cup of soil, that could explain it. So, fall sampling of soybean fields is useful for looking back and explaining yields.”The next strategy for fall SCN sampling is to pull soil samples from cornfields that were just harvested.“Assuming you’re following a corn-soybean rotation, what better time to test and see what’s coming up for your crop next season?” says Tylka.

SCN sampling guidelines

Tylka provided these sampling guidelines:

• Using a soil probe, not a spade, collect soil cores, which should be about 8 inches deep.
• Collect 15 to 20 soil cores from every 20 acres. The more soil cores collected from smaller areas, the more accurate the results will be.
• Soil cores should be collected from agronomically logical areas or management zones in the fields.
• Combine all soil cores representing a sampling area and mix well, then pour the mixed soil into a soil sample bag or plastic bag.
• SCN samples can be submitted to Iowa State University’s Plant and Insect Diagnostic Clinic, Room 2445 of the Advanced Teaching and Research Building, 2213 Pammel Drive, Ames, Iowa 50011. More information can be found by visiting here.
• Private soil-testing labs can also process samples for SCN. Information on those labs can be found by visiting the SCN Coalition’s SCN state testing labs site.

It's a SNAP to manage SCN

After receiving your fall soil sample results, managing SCN could be a “SNAP.”

Tylka encourages farmers to follow this acronym while making SCN management decisions for 2026 and beyond.

Start using varieties with Peking resistance in SCN-infested fields. Seed companies have 196 Peking-resistant varieties available for 2026.

Never grow Peking-resistant varieties twice in a row. Peking-resistant varieties will lose their effectiveness if overused.

Always grow varieties with PI 88788 resistance after growing Peking resistance.

Plant corn every year after growing a SCN-resistant variety.

“Farmers need to review the available resources and carefully consider their options for resistant varieties and seed treatments,” Tylka says.

Know your options

Tylka recommends that farmers explore all SCN management choices. To help Iowa farmers know what their options are, Iowa State University annually compiles information about SCN-resistant soybean varieties for Iowa. The list has recently been updated, and a preliminary version is available here.

For the 2026 cropping season, Iowa farmers can choose from 908 SCN-resistant varieties. The varieties for 2026 are from 35 different brands sold by 25 seed companies. Most of the varieties have one or more herbicide resistance/tolerance technologies, but 90 varieties (10%) do not.

“Information includes details like the maturity group, herbicide resistance, iron chlorosis tolerance, and most importantly, the SCN resistance genetics Peking or PI88788,” says Tylka. “Farmers should look at the publication, as it will provide their options for varieties, along with guidance from the seed companies they work with.”

Seed treatments

Nematode-protectant seed treatments are another key tool farmers should consider heading into next season.
“There are several different options available, both chemical and biological,” says Tylka. “Farmers should visit with their dealers, research these products, understand their costs, and look for online data showing how effective they are. All of this helps set up fields for success next year.”

On-farm trials

ISA has conducted several on-farm trials evaluating products designed to help control SCN. While results have been mixed, each effort provides valuable insight into managing the pest.
During a trial evaluating nematode-protectant seed treatments, no significant yield response was observed.

 “Our findings haven’t been anything monumental showing that one product does an exceptional job at reducing pressure,” says De Bruin, adding trials were in low-pressure areas, and that may have contributed to not seeing any striking results.

 De Bruin encourages farmers to test these products for themselves. And if they are interested in testing new products, ISA can assist.

 “If someone has a product they want to try, we’re more than happy to work with them to set up a good trial layout,” De Bruin says. “That way, they can collect meaningful data and determine whether or not there’s a difference.”

Stop the spread

Consider conservation efforts, such as cover crops, to help slow the spread of SCN.

“We’ve proven that windblown soil can move soybean cyst nematode,” says Tylka, who plans to continue researching the topic. It’s work he says that may open some farmers’ eyes to SCN management.

SCN Profit Checker

The SCN Coalition has created a tool for farmers and crop advisors. The SCN Profit Checker helps growers calculate how much SCN is costing them due to reduced effectiveness of PI 88788 resistance.

Using data from more than 35,000 Iowa State University research plots, funded in part by soy checkoff investments, the tool highlights the economic costs, field by field, which stresses the need for active SCN management.
For more information on SCN management, visit the SCN Coalition website. To inquire about an SCN trial, contact an ISA research agronomist at agronomy@iasoybeans.com.

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