Soybean cyst nematode (SCN) is one of the most damaging soybean pathogens in the U.S. If left unaddressed, it can be devastating to crop yields.

Dr. Sam Markell, plant pathologist and interim assistant director of the Department of Agricultural and Natural Resources at North Dakota State University, recently described the challenges of dealing with SCN.

“Soybean plants stricken with SCN are kind of like a person suffering from a tapeworm. The tapeworm normally won’t kill its host, but it will certainly keep it from doing well.” He explained that the parasitic nematode lives on the roots of plants, feeding on the plants while intercepting water and nutrients.

SCN thrives in soils with a high pH. “It likes it best where it’s warm and dry. Here [in the Midwest] it can be arid, which is conducive to it,” he said, “but in the South, which is much wetter, [and in other regions with more rainfall], it doesn’t seem to be as much of a problem.”

He said one major problem with SCN is detection. “It’s very difficult to see the damage above ground. Unfortunately, damage to a crop yield can be in the 30% range before any signs of yellowing show above the roots.”

Take the test, beat the pest

Dr. Sam Markell, a plant pathologist at North Dakota State University, is teaching farmers how to prevent and mitigate crop yield loss due to soybean cyst nematode. Photo courtesy of Sam Markell

Markell stressed that farmers should be vigilant. “Testing is important. I recommend soil sampling in the fall right before the harvest or at harvest time, when the reading levels are at their peak,” he said. Markell works with the SCN Coalition, a partnership of American and Canadian university scientists, several soybean promotion boards and private corporations to increase the number of soybean growers actively managing SCN. He said that any farmers interested in soil sampling should reach out to the organization.

“A common manner that SCN is spread is through farm equipment. It’s so important that when a soybean grower buys used farm equipment they clean it,” he said. Since SCN is soilborne, it pays for planters to purge any possible parasites when they purchase that pre-owned plow.

It normally takes multiple growing seasons for SCN to reach a level where it can damage crop yields, so mitigation measures can be taken. “Crop rotation is an option. But what we really recommend is selecting soybeans that have a good genetic resistance to SCN,” he said. Markell pointed to a breeding line named PI 88788 that has a strong resistance to SCN. “It’s been around since the 1990s. Over 90% of SCN-resistant soybeans contain PI 88788. Unfortunately, SCN has been adapting to it. It’s a little like everyone having strep throat, but the penicillin’s not working as well anymore.” Researchers are currently attempting to identify new breeding lines with stronger SCN resistance.

Markell advised farmers to remember the SCN Coalition’s motto: “Take the test, beat the pest!”

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by Enrico Villamaino