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SCN Starting to Resist SCN-Resistant Varieties
Looking for something free?
If you’re a soybean farmer, you’ve had a sweet deal without even knowing it if you’ve planted varieties that resist soybean cyst nematode (SCN).
For the most part, farmers have paid no premium for this resistance. Meanwhile, their yields have zoomed on SCN-infested soils.
On these fields, there can be up to a 15-bushel-per-acre difference in yield between SCN-susceptible and SCN-resistant varieties, says Greg Tylka, Iowa State University (ISU) Extension nematologist. Tylka discussed SCN and SCN-resistant varieties earlier this month at ISU’s Integrated Crop Management Conference.
“There is no extra cost for this management strategy,” he says.
Resistance to Resistance
Not all is rosy, though, with SCN-resistant soybean varieties. Around 97% to 98% of today’s SCN-resistant varieties share the PI88788 resistance source. Planting this same resistance source continually is akin to farmers applying the same herbicide over and over again.
“This is the equivalent of glyphosate resistance (with weeds) occurring with soybean cyst nematode resistance (to SCN-resistant varieties),” says Tylka.
As a result, farmers may find SCN resisting their SCN-resistant soybean varieties.
“We are not in a disaster zone,” says Tylka. “The PI88788 varieties are still yielding moderately well. But it is a slow decline. It’s a train wreck in slow motion.”
Why Not Other Resistance?
In the mid-2000s, varieties containing other SCN-resistance sources were increasing. “Then the bottom fell out in 2006,” he says.
At that time, Cyst-X was a popular resistance source that some companies had placed in breeding programs.
“Cyst X had great SCN resistance, but Cyst X was also resistant to yield,” says Tylka.
Anything coming up?
This won’t turn around overnight. Peking is an alternative resistance source, making up 23 of 875 SCN-resistant varieties in Iowa this year. Another avenue is transgenic SCN resistance, which several companies are researching.
Unlike current resistance, though, transgenic resistance won’t come for free. “I guarantee you will pay a transgenic tech fee,” says Tylka.
In the meantime, there are some promising seed treatments that can help farmers manage SCN.
One point that has been helping farmers for the past several years is unfavorable weather for SCN.
“Environment is the ultimate trump card,” he says. “In hot, dry weather, SCN will damage yield. But in a wet year, nematodes will be swimming.”