The soybean cyst nematode (SCN), Heterodera glycines, is the most economically significant pathogen of soybeans in the United States, accounting for an estimated 48 million bushels of yield loss annually. The second stage juvenile infects the root, penetrates the xylem and establishes a feeding site, siphoning off plant nutrients thus restricting plant growth and suppressing nodulation. SCN feeding injury also provides a point of entry for other plant pathogens to infect the root system, most notably Sudden Death Syndrome (SDS).  

SCN cannot be eradicated and must be managed using a systems approach targeted to keeping populations at manageable levels.  The foundation of your SCN management program should be a routine sampling and scouting program to understand population dynamics.  Management decisions for SCN must be done mostly BEFORE planting.  The approach includes a combination of good cultural practices, such as crop rotation, avoiding additive stressors, controlling winter annual weeds, and selecting resistant soybean varieties and seed treatments.  Crop rotation to non-host species disrupts the nematode life cycle and may decrease SCN populations. However because cysts can survive in the soil for many years, longer rotations are necessary to significantly impact population levels. This is not always practical and if soybeans are to be planted, SCN resistant varieties are an effective strategy to fend off SCN feeding and damage.  Most commercially available soybeans have been selected for naturally occurring genetic resistance to SCN, but the vast majority (95%) is from a single genetic source, PI88788. Planting varieties with the same source of resistance has resulted in SCN gradually becoming resistant to the resistance.  If you have been growing varieties with the same source of resistance and your yields are lower than expected and high numbers of cysts are found on soybean roots, it can be an indication that the SCN population is shifting. In growing environments with high SCN population pressure or resistant races, resistant varieties alone may not provide adequate control.

Fortunately, we now also have some new crop protection alternatives for SCN management.  They can help protect the roots from SCN damage by creating a feeding barrier or by directly affecting SCN’s biological functions. Commercial seed treatment products include Clariva, Avicta, Ilevo, Votivo and Aveo.  Clariva (Syngenta), contains the soil bacterium Pasteuria nishizawe which produces spores that attach to the outer layer of SCN. University and on-farm trials across the Midwest have showna range of yield responses, but the most consistent and value-added response was in situations with high SCN pressure and high yield potential. Avicta (Syngenta) contains Abamectin a fermentation product of Streptomyces avermitilis (a soil bacterium). Avicta is not systemic but it moves on the root surface as roots develop. Votivo (Bayer) is a biological product (Bacillus firmus) that does not kill the nematodes but instead acts as a repellant or a barrier to SCN feeding. Ilevo (Bayer) contains the active ingredient fluopyram. Its primary target is SDS but it has nematicidal activity against SCN and other plant parasitic nematodes. Aveo (Valent) is also a biological product but its specific mode of action is unknown.

SCN resistant varieties and seed treatments should not be viewed as stand-alone methods to manage SCN. Effective SCN management involves the integration of various tools including effective rotations along with proper agronomic practices that minimize plant stress.  Seed treatments can help improve the performance of SCN resistant varieties in situations where SCN is becoming resistant to the resistance.