Survey Results Show Continued Spread of Soybean Cyst Nematodes

By Cami Koons

Soybean cyst nematodes have been present in every Iowa county since 2017 and new survey results show the costly crop pests continue to spread to more counties across the country and in Canada. 

Greg Tylka, a nematologist at Iowa State University, led the survey that has monitored the spread of soybean cyst nematodes, or SCN, since 2014, and found 31 counties in 10 states reported SCN for the first time between 2020 and 2023. 

“It’s reasonable to conclude that increased soybean yield losses due to the nematode will follow, if not already occurring in these areas,” Tylka said in a press release about the new report.

Soybean cyst nematodes are estimated to cost farmers close to $1.5 billion in lost profits, annually in North America. 

SCN infestations are not always evident as the fields will often look healthy, even while the nematodes are rapidly generating, infesting the roots of the soybeans and limiting the plant’s ability to absorb nutrients and produce beans.

SCN can also exasperate the effects of crop diseases, like sudden death syndrome, by causing additional stress to the plants.

Tylka hopes the survey results will alert farmers of the presence in their counties so they know to get a soil test and figure out how to farm with SCN. 

There is little a farmer can do to prevent SCN from entering or leaving a soybean field. The nematodes live in the soil and therefore can spread anytime soil moves. Even a dust storm could carry SCN from one county to the next.  

There is also no way to completely eliminate SCN from a field, so farmers have to rely on crop rotations and SCN resistant soybean varieties to minimize the effects of SCN.

Rotating corn into the field helps to manage some of the SCN population since the nematodes will only feed on soybeans. 

Soybean varieties with PI 88788 genetics have been the dominant SCN resistant varieties for the past several decades, but SCN populations have begun to develop a resistance to PI 88788 due to its heavy use. 

Tylka’s research with ISU showed that the number of SCN resistant varieties using Peking genetics have more than doubled from 2023 to 2024, which he said gives farmers more opportunity to rotate Peking and PI 88788 varieties. 

Tylka said at a media event in November 2024 that the rotation of SCN resistant varieties is vital to the long-term management of the nematodes, as it will prolong the time it will take SCN populations to develop resistance. 

“I am terrified about losing Peking,” Tylka said, noting that while Peking has good resistance now, it will probably lose effectiveness within five to six seasons. 

“My message is, farmers must not abandon 88788, but rotate it with Peking,” Tylka said. 

Farmers can also make use of fall soil tests that measure SCN presence and resources from the SCN Coalition, including a profit checker, that estimates a farmer’s losses per field due to SCN factors. 

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