Understanding Detection, Prevention, and Management of Soybeans’ Most Costly Pest

Soybean cyst nematode (SCN), Heterodera glycines, remains the most damaging pathogen affecting soybeans in North America, costing U.S. farmers more than one billion dollars in lost yield annually. Updated national surveys confirm that SCN has now been detected in every soybean producing state in the United States except West Virginia, underscoring how widespread the pest has become. 

Research coordinated by Iowa State University and the SCN Coalition shows that SCN distribution has steadily expanded over the past several decades. Although the rate of new county detections has slowed, most major soybean growing regions overlap directly with known SCN infestations. Experts caution that the absence of detection does not mean fields are free of SCN, as infestations can remain undetected for years without routine soil testing. 

(For Canadian farmers, SCN has been detected in Ontario, Manitoba, and Quebec.)

Soil Sampling Is the Only Reliable Method for Farmers to Detect Soybean Cyst Nematode
SCN cannot be accurately identified based on above ground symptoms alone. Many infested fields show no visible damage while still experiencing significant yield loss. Soil sampling remains the most reliable method for detecting SCN and measuring population levels. 

Best practices for SCN soil sampling include:

• Collecting soil samples in the fall after harvest or in the spring before planting
• Sampling high risk areas, such as field entrances, low yield zones, and compacted areas
• Submitting samples to a qualified diagnostic laboratory for egg counts

Early detection allows farmers to make informed decisions on variety selection, crop rotation, and additional management strategies before yield losses escalate. 

Root Inspections Can Provide Clues
In-season scouting may reveal small white or yellow cysts attached to soybean roots, about the size of a grain of sand. While this method can confirm infestation, it often appears only after populations are already established and yield loss may have occurred. 

Preventing the Spread of SCN
1. Limit Soil Movement - SCN spreads primarily through the movement of infested soil. Farm equipment, vehicles, water runoff, wind, and even footwear can transfer cysts between fields. Cleaning equipment when moving from known infested fields to clean fields is an important preventive measure. 

2. Rotate Crops Strategically - Crop rotation with non host crops such as corn, wheat, sorghum, or alfalfa remains one of the most effective ways to reduce SCN population densities over time. While rotation does not eliminate SCN, it can significantly reduce egg counts and slow population buildup. 

3. Avoid Continuous Soybean Production - Fields planted to soybeans year after year experience faster SCN population growth. Continuous soybean production accelerates reproduction and increases pressure on resistant varieties, reducing their long term effectiveness. 

To Tackle SCN Once It Is Detected Use Resistant Soybean Varieties, but Rotate Resistance Sources
Planting SCN resistant soybean varieties remains the cornerstone of management. However, most resistant varieties in North America rely on the PI 88788 resistance source. Decades of heavy use have allowed SCN populations to adapt, reducing the effectiveness of this resistance in many fields. 

Farmers are encouraged to:

• Rotate between resistance sources such as PI 88788 and Peking when available
• Avoid planting the same resistance source in successive soybean crops
• Consult local variety trial data to evaluate SCN resistance performance

Incorporate Seed Treatments Where Appropriate
Nematicide seed treatments can provide early season root protection and help limit yield loss, particularly in fields with moderate to high SCN populations. These products work best when used in combination with resistant varieties and sound rotation practices. 

Monitor Fields Regularly
SCN management is not a one time decision. Regular soil sampling every three to four years, or more frequently in high risk fields, helps track population trends and evaluate whether management practices are working. 

The Bottom Line for 2026 Soybean Production
With SCN now detected in nearly every soybean producing state, proactive management is no longer optional. Early detection through soil sampling, prevention through crop rotation and sanitation, and active management using rotated resistance sources are essential steps to protecting soybean yield potential.

As researchers continue to update national SCN distribution maps and develop new management tools, farmers who remain vigilant and adaptive will be best positioned to stay ahead of the most costly soybean pest in North America.