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Tips for choosing SCN-resistant soybean varietiesTips for choosing SCN-resistant soybean varieties

There are more SCN-resistant soybean varieties than ever, but diversity of resistance is lacking.

Rod Swoboda 1

October 28, 2016

3 Min Read

Nearly 40 years after its discovery in the upper Midwest, the soybean cyst nematode (SCN) continues to be a highly damaging pathogen of soybeans in Iowa and surrounding soybean-producing states. SCN is a tiny, microscopic worm that attacks soybean roots and steals yield.


SCN is most damaging in hot, dry growing seasons, but yield losses of 10% to 25% or more can occur in years when temperatures are moderate and rainfall is average or above average. That’s according to Greg Tylka, Iowa State University Extension plant pathologist and nematologist. “Growing SCN-resistant soybean varieties can slow the build-up of SCN population densities (numbers) in the soil and produce profitable soybean yields in SCN-infested fields,” says Tylka. He offers the following information and advice on choosing SCN resistant varieties to plant on your farm in 2017.

Lots of choices are available for farmers to plant

Each year, Iowa State University compiles a list of SCN-resistant soybean varieties that are available to Iowa farmers. The list was just recently updated. This effort is funded by the soybean checkoff through the Iowa Soybean Association. The publication is available to download for free here from the ISU Extension Publication store.

There are more than 950 varieties from 34 seed companies and ISU included in the publication. The source of SCN resistance, relative maturity rating, herbicide resistance, and iron deficiency chlorosis tolerance of the varieties are included in the list.

However, there’s not much diversity of resistance

Although there are many SCN-resistant varieties available for Iowa soybean farmers, almost all (97%) contain resistance genes from a single soybean breeding line, named PI 88788 (see figure below). There are 81 more SCN-resistant soybean varieties in the 2016 publication than there were in 2015, but only two more SCN-resistant varieties with resistance from a source other than PI 88788 than in 2015. The prolonged, widespread use of PI 88788 SCN resistance genes has led to selection for SCN populations with increased reproduction on varieties with the PI 88788 source of resistance.

Tips for choosing SCN-resistant soybean varieties

Figure 1. Number of SCN-resistant soybean varieties in maturity groups 0, 1, 2, and 3 for Iowa soybean farmers, 1991 to 2016.

All SCN-resistant soybean varieties are not created equal

Resistance to SCN in soybeans is provided by several genes, and not every resistant soybean variety receives all of the resistance genes during the breeding process, even if they are bred from the same resistance source, such as PI 88788. Consequently, not all SCN-resistant soybean varieties provide the same level of nematode control.

ISU has annually evaluated nematode control and yield of SCN-resistant varieties in numerous field experiment conducted in SCN-infested fields throughout Iowa since the early 1990s. The work currently is funded by the soybean checkoff through the Iowa Soybean Association.

Results of the variety evaluation experiments are compiled in an annual report that is printed and mailed throughout Iowa via the media. The report also is available to download for free here from the ISU Extension Publication store. Finally, the variety trial result reports dating back to 1997 are available online at isuscntrials.info.

More information about the biology and management of SCN available at soybeancyst.info and at soybeanresearchinfo.com/diseases/scn.html.

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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