Soybean rows

When rounding up data for the annual soybean cyst nematode yield tests, Iowa State University plant pathologist Gregory Tylka said results were surprisingly good.

Yields in nine statewide experiments reached as high as 81 bushels per acre this year. But when examining SCN, Tylka noted there is still a significant presence.

“We still saw significant reproduction of soybean cyst nematode on most resistant soybeans across those locations as well,” he said.

He said that while all types of soybeans that had SCN resistance yielded better than those without, there was a variety that stuck out. The more common resistance source, PI88788, did not perform as consistently well as Peking resistance, which is only found in about 5% of soybean varieties.

Tylka said the genes found in the PI88788 variety have been around for 25-30 years. He compared this to using the same herbicide on weeds for a long period. Over time, the weed develops resistance and is more difficult to keep at bay.

“What we are seeing every year, more and more, is the varieties with Peking resistance yielding higher and higher in the overall rank of things,” he said. “And that’s nothing to do with the genetics of the soybean varieties, and everything to do with the nematode becoming resistant to resistance.”

Over the last five to seven years, the soybeans with Peking resistance have become one of the more consistent top yielding varieties, Tylka said. The results in their southeast Iowa location showed just how drastic the difference could be in some scenarios.

“We had 67 varieties with PI88788 and two varieties with Peking resistance, and those two Peking varieties finished as the top two,” Tylka said. “Those two Peking varieties yielded 73 and 71 bushels per acre, and the next highest yield, the top yielding PI88788, was 58.7 bushels per acre. That’s 14 bushels less.”

He said if soybeans are priced at $9, that would amount to a nearly $126 per acre difference.

“That’s breathtaking,” Tylka said.

The southeast Iowa yield test featured the sandiest soils for the tests, a characteristic which tends to promote nematode reproduction, Tylka said, so the additional presence of nematodes may impact the results.

He would like to see more options for farmers from seed dealers, as he said nearly 95% of SCN-resistant soybean varieties available use the PI88788 genes.

“My message to farmers is to start demanding (Peking) from the seed companies,” he said. “I don’t think a seed company is going to react to my message, but hopefully they will react to their customers.”

Tylka said weather didn’t play much of a factor in their research this year, which came as a surprise to him, considering how variable weather was across the state of Iowa.

A special section in this issue of Iowa Farmer Today contains more results of the Iowa State University SCN yield tests.

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