By the SCN Coalition
A hot topic at the North Central Soybean Research Program, 2022 National Soybean Nematode Conference was a new genetic tool for managing soybean cyst nematode (SCN) that’s expected to hit the market late this decade. “The new Bt SCN resistance trait developed by BASF will slow the rate of increasing yield loss, but it alone won’t fix the problem,” says Greg Tylka, nematologist at Iowa State University and a leader of The SCN Coalition. The mounting economic toll of parasitic nematodes must not be met with complacency. Barring the unexpected development of a silver bullet, an active, multipronged defense against SCN will be needed.
SCN currently costs farmers 5.5 bushels an acre, equating to roughly $1.5 billion in yield loss each year, estimates Mike McCarville, trait development manager at BASF. By 2030, he expects that yield reduction to grow to “about 10 bushels an acre, amounting to over $2 billion in lost soybean yield each year.”
Farmers are planting resistant varieties, but McCarville explains that data from Tylka’s variety trials in Iowa show SCN is reproducing at around 35% on the PI 88788-based varieties that dominate the market today. McCarville expects reproduction will rise to 50% by 2030. Based on that, it might be tempting to switch completely to another source of SCN resistance known as Peking. But McCarville explains resistance management modeling shows SCN will adapt to Peking much faster than it did to PI 88788. Therefore, experts encourage farmers to rotate resistant varieties to preserve that longevity.
“This is a massive problem that requires a big solution,” McCarville says. “I believe that big solution will require new traits, and those traits will have to be partnered with other tactics and technologies to provide a sustainable solution for this pest.”
Parasitic Fungi for Biological Control of SCN
One possible avenue of defense is the development of new biocontrol strategies for SCN, an approach pursued by Kathryn Bushley, research molecular biologist and curator of the Agricultural Research Service Collection of Entomopathogenic Fungal Cultures at USDA. “The field of biological control has long focused on a single-mechanism approach,” she says. “An interactive or multi-faceted approach to agronomic threats like SCN is worth exploring.”
Bushley is studying nematode-trapping fungi that colonize in the soybean root zone, vetting them as candidates for seed coatings or root bio-inoculants for protection against SCN. In addition to trapping nematodes, Bushley says the beneficial root endophytes can also indirectly prep a plant’s defense mechanisms.
SCN Interaction with Other Pathogens
Soybean pathologist and nematologist Horacio Lopez-Nicora at The Ohio State University set the stage for his presentation with this quote: “Nature does not work in a pure culture.” A farmer rarely deals with a single pathogen. What’s more, those pathogens interact, Lopez-Nicora says.
His survey work in Ohio showed 77% of the samples collected contained SCN and Macrophomina phaseolina, the pathogen that causes soybean charcoal rot. Analysis of that data showed a significant interaction between the two that had a linear and negative impact on yield without causing visible symptoms. The yield hit was especially pronounced for fields with high populations of both pathogens. Lopez-Nicora’s findings drive home the importance of integrated pest management strategies that consider the full picture when dealing with SCN and other soilborne pathogens.
Speakers with Pattern Ag expressed similar sentiments, noting their soil sampling shows SCN-infested fields are often also infested with Pythium or Fusarium virguliforme, the agent that causes sudden death syndrome. SCN causes other diseases to be “highly expressed,” explains Pattern Ag’s Mike Tweedy. There’s a lot of farmer apathy toward SCN, but he says, “the breakthrough happens when we discuss the synergistic effect with other diseases and their impact on yield.”
Advances in technology are bringing the industry a deeper understanding of SCN and potential new avenues for fighting it – whether that’s with biocontrol agents or a focus on overall soil health or using drones for more precise management of fields. All these strategies have a place at the table, giving farmers more ways of keeping SCN on its toes.