Production Blog

More Soybean Farmers Rotating SCN Varieties

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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The growing season is a good time to dig some soybean roots to see if you can see soybean cyst nematode. A hand lens can help spot the tiny white females that appear like grains of sand on the soybean root. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- Soybean farmers appear to be getting the message that they must manage soybean cyst nematode (SCN) resistance to avoid yield losses. A 2020 survey showed that 49% are now rotating sources of genetic SCN resistance. Of those farmers rotating genetic sources, 25% identified Peking as their alternative source of SCN resistance.

The survey of nearly 1,000 soybean growers in 17 states was funded by The United Soybean Board to monitor outreach by The SCN Coalition. A similar 2015 survey revealed only 39% of farmers were rotating genetic sources of SCN resistance. At the time, genetic resistance known as PI 88788 was used in 95% of the commercially available soybean varieties. Overuse of that one source of resistance has become one of the battle cries of the industry in efforts to manage the No. 1 yield-grabbing pathogen in North American soybeans.

The 2020 study results released this week found:

-- 49% of growers said they were rotating sources of genetic SCN resistance, up from 39% in 2015.

-- 25% of growers identified Peking as their source of SCN resistance up from 15% in 2015.

-- 40% of growers said they use a nematode-protectant seed treatment, up from 22% in 2015.

-- 77% of growers said they were rotating non-host crops such as corn and wheat, up from 71% in 2015.

-- 66% of growers said they were planting SCN-resistant soybean varieties, up from 59% in 2015.

Soybean growers also reported they perceive SCN reduces yield by 5.1 bushels per acre. However, Iowa State University data from 15 years of variety trial experiments in growers' fields has revealed increased reproduction of SCN populations on PI 88788-resistant varieties can decrease yield by as much as 14 bushels per acre.

Do the math on those losses at today's prices and the incentive to manage SCN quickly emerges. Based on the USDA's May WASDE 2021 soybean price projection of $13.85 per bushel, a 5.1-bushel-per-acre yield loss represents leaving $70.64 per acre in the field.

The SCN Coalition includes university scientists from 28 U.S. states and Ontario, Canada, grower checkoff organizations including the North Central Soybean Research Program, United Soybean Board and several state soybean promotion boards, and corporate partners including BASF, Bayer, Growmark, Nufarm, Pioneer (Corteva), Syngenta, Valent and Winfield United.

Want to learn more about SCN management? The coalition has developed a website and video series called "Let's Talk Todes" featuring scientists and soybean growers. Find it here:….

Find more information on how SCN continues to move into new geographical regions here:….

More about the decline of PI 88788 and new Bt traits that might help can be found here:….

Learn how nematodes hitchhike into fields:….

A look at southern nematode issues can be found:….

Visit to learn more about actively managing SCN and to get recommendations specific to your state provided by university and Extension experts.

Pamela Smith can be reached at

Follow her on Twitter @PamSmithDTN


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