Soybean Cyst Nematode in 2019 and Beyond

The soybean cyst nematode (SCN) was first found in the United States in North Carolina in 1954, and it was discovered in the upper Midwest in the late 1970s. The nematode is one of the most damaging pathogens of soybeans in the United States. SCN was first found in many counties and states in the Midwest in the 1980s. The 1990s was a decade in which scouting and soil sampling for SCN was frequent. Many farmers’ fields were first discovered to be infested with SCN in these years, and widespread management of the nematode began. Managing SCN in the 2000s was as simple as 1) pick a resistant variety, 2) plant it, and 3) forget about SCN. Unfortunately, that no longer is the case. Currently, the effectiveness of SCN resistance is eroding. Almost all of the SCN-resistant soybean varieties ever grown in the United States have had resistance genes from a soybean breeding line called PI 88788. And many (or most) SCN populations in the Midwest now have built up the ability to feed and reproduce on that resistance. What will happen with SCN in 2019 and beyond? All is not lost. The common PI 88788 resistance is widely available in current soybean varieties and it still offers some SCN control, just not high levels of control. So in general, soybean varieties with PI 88788 resistance should not suffer as much yield loss as susceptible (non-resistant) soybeans, but yields of the resistant varieties will be reduced by SCN. There are a few soybean varieties with resistance from a breeding line called Peking, and more varieties with the Peking resistance will become available in the near future. Peking resistance currently controls most SCN populations much better than the PI 88788 resistance. Also, yields of varieties with Peking SCN resistance will be greater than varieties with PI 88788 resistance when grown in fields with SCN populations that have high reproduction on PI 88788 resistance. There are a few soybean varieties being developed with a source of resistance called Hartwig that may be helpful in managing SCN, and scientists are working to develop genetically engineered SCN resistance. Finally, several nematode-protectant seed treatments have been introduced in the last 10 years, and additional new seed treatments will become available in the future. The seed treatments have different modes of action, and their effects on SCN population densities and on soybean yields have been variable. In summary, managing SCN for the long term requires a multi-faceted approach using every management option available. And periodically determining SCN numbers through soil sampling also is necessary to assess the success of management efforts.