COLUMBUS, Ohio – Researchers from the Ohio State University and OSU Extension specialists recommend that soybean growers check roots for the presence of soybean cyst nematode (SCN) through September. SCN has been detected in 71 counties across Ohio, with the highest concentrations in the northwest. Although plants infested with SCN can present with yellowing leaves and necrosis, it is more common that growers will notice no above-ground symptoms.

“Soybean cyst nematode is the most economically damaging pathogen of soybean in North America, for sure,” Horacio Lopez-Nicora, assistant professor of soybean pathology and nematology at OSU, said. “The reason is that it can cause significant yield reduction without any visible symptoms. So, soybeans can look really healthy, yet have more than 30 percent yield reduction.”

Proactive management is the best way to combat SCN, so researchers recommend checking plants for the presence of SCN. One way to do so is by collecting a soil sample and sending it to a nematology lab. With the support of the Ohio Soybean Council, OSU offers soybean growers the opportunity to submit up to two soil samples to the Soybean Pathology and Nematology Lab for free SCN testing. After the sample has been analyzed, growers will know if SCN is present, and the number of eggs found.

Another way growers can check for SCN is by digging up plants and checking the root systems for the nematode’s namesake, cysts. After the nematodes mate, female worms produce about 50 eggs outside of its body and fill up with 200 or more eggs internally. The female then dies, with the body hardening to form a cyst, which is small and white in appearance. While cysts are visible to the naked eye, it may be helpful to use a lens to look closer. Producers should not confuse larger, nitrogen-fixing nodules with SCN.

Knowing SCN numbers is incredibly important for producers. The SCN life cycle is about 24 days long, and there can be three to six generations yearly. According to the SCN Coalition, even with an attrition rate of 99 percent, meaning only 1 percent of eggs survive each generation, 39,062 eggs could be present at the end of the growing season.

Researchers and specialists offer different management strategies based on the number of SCN eggs present. For example, Lopez-Nicora said that if a soil sample reported 5,000 eggs per 100 cubic centimeters, the recommendation for the grower would be to rotate growing a non-host crop, like corn, and then rotate resistant soybean varieties. Additionally, growers may be recommended to use a nematode-protectant seed treatment, which shields the plant from SCN.

More than 90 percent of all commercially available soybeans resistant to SCN use breeding line PI 88788, which has been used for over two decades. Historically, PI 88788 has been an excellent tool for controlling SCN until the worms adapted. Lopez-Nicora said that PI 88788 was effective at getting rid of the SCN population that the resistance works well for, but indirectly helped to grow a population of SCN that can reproduce on PI 88788.

“We have populations (of SCN) in Ohio where the female index, which measures relative reproduction to a susceptible host, is 80 percent. So, the population we have here when we plant PI 88788, SCN can reproduce at 80 percent compared to a susceptible variety,” Lopez-Nicora said. “So, (the plant) is really 20 percent resistant to SCN. That’s really not resistant anymore.”

Another breeding line called Peking also offers resistance to SCN. Still, Lopez-Nicora cautioned against becoming overly reliant on a different line than PI 88788: “You don’t want to get into the same issue where you grab Peking and keep using it and shift the virulence of the population.”

Lopez-Nicora said that understanding the mechanism by which soybean plants resist SCN is a critical part of the puzzle for researchers hoping to find new solutions. Researchers from the University of Georgia and the University of Missouri discovered that nematodes reproducing on Peking genetic resistance exploited one particular gene. Through gene editing, researchers found they could add a nonfunctioning copy of the gene to enhance the plant’s SCN resistance. Now, the research group must test whether the genetic edit impacts yield, an important question before commercialization is pursued.

In June, BASF, a chemical corporation, debuted Nemasphere, a nematode resistance trait. According to BASF field trials, Nemasphere can be incorporated into a range of high-yielding seed varieties and boosts yield potential by 8 percent. BASF plans to make soybean varieties containing the trait available in 2028, pending regulatory approval.

OSU is also diligently working to find solutions for producers. Lopez-Nicora said that the university uses data it receives in the lab to understand what types of nematodes are found in the soil and what areas in the state are at risk. He said that research groups evaluate different seed treatments and genetic materials to find the most effective management strategies.

Lopez-Nicora also mentors and trains students at the university working on various projects related to SCN. One student is investigating the interaction between SCN and other pathogens like fungi to understand how the presence of multiple pathogens impacts growth. Another student is working on automated sampling and using a machine to take samples more precisely so that intensive maps of the distribution of nematodes in a field can be created to inform precision management.

Overall, Lopez-Nicora encourages growers to become involved in research to aid in the battle against SCN. OSU and its extension offices are committed to listening to the needs and questions of growers while allowing the opportunity to participate in research.

“It’s a two-way communication. Growers are our most important stakeholders,” he said. “The research program works for them and with them.”