SCN Native Resistance Erodes  09/18 10:44

   Better SCN Management and a New Trait Can Help Combat the Top Soybean Yield 
Robber

   A new study found that the most widely used trait to combat SCN, PI 88788, 
continues to lose its effectiveness. Better management and vigilance are needed 
to safeguard native SCN resistant traits. However, a new transgenic trait is on 
the horizon to combat the No. 1 yield robbing soybean pest.

Matthew Wilde
DTN Crops Editor

   BOONE, Iowa (DTN) -- Call Greg Tylka the "soothsayer of SCN."

   About 10 years ago, the Iowa State University (ISU) nematologist and leading 
soybean cyst nematode (SCN) expert predicted that the most widely used trait to 
combat the pest - PI 88788 - would continue to lose its effectiveness. An ISU 
study released in late August confirmed his prognostication.

   "If you are a biologist and study selection pressure, that's no surprise. In 
fact, it's pretty easy to predict," Tylka said during an SCN panel discussion 
at the Farm Progress Show near Boone, Iowa, earlier this month.

   Tylka, Dylan Mangel, a University of Nebraska soybean plant pathologist and 
co-leader of the SCN Coalition, and Austin Behrendsen, a farmer near 
Pocahontas, Iowa, discussed SCN and management strategies. BASF hosted the 
panel.

   First detected in the United States in the 1950s, SCN is the No. 1 
yield-robbing soybean pest, costing farmers an estimated $1.5 billion annually, 
according to the SCN Coalition, a public/private/checkoff partnership formed to 
increase the number of growers actively managing the nematode. The parasitic 
worm feeds on soybean roots, inhibiting plant growth and reducing root function.

   Since the late 1980s, PI 88788 has been the primary SCN resistance source in 
U.S. soybeans due to its initial effectiveness and yield potential. Overuse and 
the ability of SCN to adapt continue to erode its effectiveness.

   Recently released ISU field trial data collected from 2001 through 2023 
revealed that the ability of SCN populations to reproduce on PI 88788 
resistance increased 2% annually. SCN virulence to the trait is increasing at a 
nearly identical rate as a decade ago. All the data was collected in Iowa, 
though Tylka said the results are not unique to the state.

   Based on the data, researchers project that PI 88788 resistance may provide 
only about 40% SCN control by the end of the decade, leaving growers vulnerable 
to average yield losses of roughly 9 bushels per acre (bpa), equivalent to 12% 
of yield potential.

   "If we don't diversify how we manage the pest, farmers can expect that trend 
to continue," Tylka said in a statement.

   Find the ISU SCN study at 
https://www.thescncoalition.com/news/2026/08/19/scn--adapts--pi--88788--resistan
ce/.

   WAKE-UP CALL

   Behrendsen agrees that better stewardship of SCN traits is a must. His 
wake-up call about the declining efficacy of PI 88788 came several years ago 
when he noticed a 15- to 20-bpa yield gap between two soybean fields located 
about a half a mile apart. After digging deeper, he learned the lower-yielding 
field was planted to a variety with PI 88788 resistance, while the 
stronger-performing field was a variety with Peking (PI 548402) resistance.

   Peking is currently the only other SCN resistant breeding line used in 
soybean varieties. It became more widely commercially available five years ago. 
While highly effective, Tylka said it's only available in 20% of soybean seed 
offerings to date.

   Behrendsen is taking steps to boost bean yields and protect SCN resistant 
traits, including collaborating with ISU on SCN research.

   "Rotating varieties is so important. You don't want to plant Peking year 
over year, or SCN will become resistant to that (trait) faster," Behrendsen 
told DTN.

   MANAGEMENT STRATEGIES

   The SCN Coalition and panelists recommend several steps farmers can take to 
better manage the pest and preserve trait efficacy.

   Test soil for SCN after harvest to know your egg numbers. Enter those 
results in the SCN Profit Checker to better understand potential yield loss and 
profit risk. Find the checker at 
https://www.thescncoalition.com/profitchecker/calculator/.

   Consider planting corn-on-corn if SCN egg counts in a field exceed 10,000 
per half a cup of soil, Tylka said. That will help reduce SCN pressure.

   Adopt a balanced soybean rotation that includes both PI 88788 and Peking to 
slow the development of virulent SCN populations while maintaining yield 
performance. In a corn-soybean rotation, a field would be planted to one of the 
traits once every three years. In a corn-soybean rotation, rotating traits will 
extend the effectiveness of Peking to 20 years instead of 10 if Peking is 
solely used, Tylka estimates. Effective SCN resistance in soybeans is defined 
as 90% or more control.

   "I fear the farmers that go for maximum yield in the short term (and only 
plant Peking) will hurt themselves in the long term," Tylka told DTN. "Rotation 
reduces SCN pressure, which will make PI 88788 more effective."

   Nematode-protectant seed treatments can complement SCN resistant varieties 
or when host plant resistance is not available. Both chemical-based seed 
treatments and biologicals are available and labeled for managing SCN.

   "When we plant PI 88788 as part of a rotation, we're more likely to spend 
money on a seed treatment to make the trait more effective," Behrendsen told 
DTN.

   Consider planting nonhost crops - corn, alfalfa, oats, etc. - to lower egg 
counts and extend trait efficacy.

   Find the SCN Coalition SCN management guide at 
https://www.thescncoalition.com/field--guides/soybean--cyst--nematode--managemen
t--guide/.

   HELP IS ON THE WAY

   BASF is on track to launch a new transgenic trait called Nemasphere to fight 
SCN in 2028, company officials recently confirmed. It will be stacked with 
native SCN-resistant traits and Enlist E3 soybean varieties.

   The company currently has 28 soybean varieties in development ranging from 
Group 0 to Group 4.5 maturity.

   Nemasphere expresses the protein Cry14Ab-1 that when ingested by the 
nematode eventually leads to its death, similar to Bt trait technologies that 
have been used for insect control in corn and soybeans previously. It's the 
first new novel mode of action to combat SCN in more than 60 years, and the 
first and only biotech trait.

   "We should have all our regulatory approvals by the end of this year. We'll 
be able to grow enough seed for a full launch in 2028," Justin Moritz, BASF 
trait technology specialist, told DTN.

   Like weeds developing resistance to herbicides, SCN has done the same thing 
to native traits, Moritz said. Soybean yields can be reduced by 30% or more by 
SCN with no above-ground visual symptomology.

   "We're really excited because Nemasphere will be paired with native traits 
to create a durable, robust SCN protection system," he added.

   Moritz expects current SCN yield losses will be mitigated in soybeans with 
the Nemasphere trait. "Growers will get back to the level on SCN control that 
they used to have with PI 88788. It's a unique system that's going to allow for 
maximum genetic (yield) potential to be expressed."

   Another reason Moritz is optimistic about the performance of Enlist E3 
soybeans with Nemasphere is that plants will tolerate a fourth herbicide: 
mesotrione, a Group 27 HHPD inhibitor. Enlist E3 soybeans also tolerate 2,4--D 
choline, glyphosate and glufosinate. Using multiple sites of action helps 
control weeds while limiting the development of herbicide-resistant weeds.

   "We know mesotrione is a really effective (weed control) tool that works 
really well from a residual standpoint," Moritz said.

   Best SCN management practices are recommended with Nemasphere Enlist E3 
soybeans, including rotating native traits. "We're all going to have to 
continue to be stewards of these technologies," he concluded.

   Read a 2024 DTN story about Nemasphere at 
https://www.dtnpf.com/agriculture/web/ag/crops/article/2024/06/10/biotech-trait-
basf-provides-novel.

   Learn more at 
https://agriculture.basf.us/crop--protection/products/seeds/nemasphere.html.

   Matthew Wilde can be reached at matt.wilde@dtn.com.

   Follow him on social media platform X @wildeagwriter




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