Soybean Roots Are Out of Sight but Top of Mind

The dual threats of Sudden Death Syndrome and soybean cyst nematode require a multipronged defense.
Soybean Roots Are Out of Sight but Top of Mind
“A wise man once told me to always bet on the pest,” says Kerry Dittbenner, sales agronomist with Central Farm Service in Lewisville, Minnesota. “They’ll always adapt.”
Find out how the dual threats of Sudden Death Syndrome and #soybean cyst nematode require a multipronged #ag defense.

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Evolution is nothing new for soybean growers. For decades, growers have battled resistant weeds and evolving disease pressure. However, two of the biggest soybean threats have been adapting and spreading where growers can’t easily see them — under the soil.

Sudden Death Syndrome (SDS) and soybean cyst nematode (SCN) hide in cool, wet soils in nearly every major soybean-growing state. While SDS and SCN attack soybeans in different ways, both can cause devastating yield losses.

“As SCN and SDS continue to adapt and spread through the U.S., growers need to be prepared to defend their yields by using every tool in their toolbox,” says Dale Ireland, Ph.D., technical product lead for Syngenta Seedcare.

As SCN and SDS continue to adapt and spread through the U.S., growers need to be prepared to defend their yields by using every tool in their toolbox.

Dale Ireland, Ph.D.
Technical Product Lead, Seedcare
A Visual Killer

SDS, a soilborne disease caused by Fusarium virguliforme, infects soybeans early. But foliar symptoms don’t appear until it’s too late to protect against yield losses, which can be as high as 80%.1

“We often forget about the first stage of the disease because we see those foliar symptoms later in the year, and that’s what catches our attention,” says Jason Bond, Ph.D., a professor and plant pathologist at Southern Illinois University. “There are a lot of Fusarium species that attack soybeans. This is one that not only attacks the roots early in the season, but also causes scorch later on because it produces a toxin that gets translocated up into the upper portions of the plant.”

These noticeable foliar symptoms begin with yellow spots on the leaves and spread into chlorotic interveinal leaf scorching. Defoliation and pod expulsion then occur, leading to potentially catastrophic yield loss.

“Growers talk to me about SDS costing them 30, 40 bushels an acre on a soybean crop,” says Zachary Trower, agronomy service representative with Syngenta. “Now that is huge and can mean the difference between turning a profit or not turning a profit on that acre.”

The Stealthy Yield Robber

On the other hand, SCN causes an estimated $1.5 billion in yield loss each year and can do it without causing visual symptoms.

“It’s so easy — especially if you’ve been dealing with SDS — to forget about the impact that SCN has just by itself,” Bond says. “In this part of the country, one thing we’ve seen consistently is the rapid adaptation of cyst nematode to resistant varieties. We’re losing anywhere from 3 to 10 bushels per acre to this pest, even when we’re planting resistant varieties in heavily infested fields.”

When SDS and SCN appear in the same field, yield loss multiplies exponentially. As SCN feeds on soybean roots, the puncture wounds from the parasite make the plant more susceptible to SDS infection.

“I think it’s more of a cumulative stress factor: One stress predisposes the plant to even greater damage because you have these two stresses together,” Bond says. “The SDS pathogen doesn’t need cyst nematode to cause damage, but we tend to get SDS symptoms a little earlier and more severely when there’s also SCN.”

Better Fix It Before It’s Broken

As with many pests and diseases, protecting against SDS and SCN begins with choosing the right resistant soybean varieties. When it comes to SCN-resistant varieties over the past 20 years, more than 90% almost exclusively relied on a single source (PI 88788). While it has been a vital tool, over-reliance on PI 88788 has resulted in a rapid loss in effectiveness over time.

Because of this ongoing challenge, Syngenta Seeds has developed a new soybean variety with a novel source of SCN resistance — PI 89772.2

NK is constantly working to introduce and rapidly scale up new SCN tools,” says Andy Heggenstaller, Ph.D., head of agronomy at Syngenta Seeds. “In our 2022 Enlist E3® soybean portfolio, almost 10% of those varieties are expected to have an alternate SCN source of resistance that most soybean acres have not yet experienced. We look to expand access to more varieties with alternative sources of SCN resistance over the next several years. For growers, this innovation means we can continue protecting their yield potential from SCN for years to come.”

One Is the Loneliest Number

SDS and SCN require a combination of strategies to protect yield. Nonhost crop rotation, SCN- and SDS-resistant genetics, and seed treatment protection should all be used to defend a grower’s return on investment.

“Since you can’t put the genie back in the bottle, we don't want to just rely on one mechanism to control SDS,” Bond says. “It’s a balance. You want to use host resistance, but you also want to consider chemical control, so you’re not just relying on one way to control the organism.”

For his customers, Alex Labenz, regional sales manager with Frontier Cooperative in Genoa, Nebraska, has tried using only resistant varieties. He’s also tried SDS seed treatments, including Saltro® fungicide seed treatment in a 2019 precommercial trial after learning that it provided an average 4-bushel-per-acre yield advantage over ILEVO® seed treatment in multistate trials over a four-year period.3 Now registered for commercial use, Saltro delivers superior SDS protection without the stress, as well as robust activity against nematodes, including SCN.

“Last year was the first time I did a trial with Saltro,” Labenz says. “It was a small, precommercial trial in a hot spot in a grower’s field. We treated 98% of that grower’s acres with a competitor. After seeing how well that little plot performed, the grower is using 100% Saltro this year, and we’re happy with how things are looking so far.”

Labenz’s results don’t surprise Ireland. “By combining Saltro with the right SDS-resistant variety, you ultimately protect your bottom line,” he says. “It can significantly reduce the risk of late-season foliar symptom expression, and the potential payoff is higher yields at harvest.”

1. “Sudden Death Syndrome,” Wisconsin Field Crops Pathology Division of Extension, University of Wisconsin-Madison,
2. “Nematologists Eager to Study a New Soybean Variety With SCN Resistance,” The SCN Coalition,
3. U.S. trials with SDS pressure; 2015-2019. Trial locations: AR, IL, IA, KS, KY, MI, MN, MO, TN, WI. Trials with significantly different disease incidence/severity rating between Check and SDS treatment.