The only way to know is to take a soil sample.
Contact your local extension office to get a soil sample bag today!
Field Symptoms - The first indication of a problem is when soybean yields are lower than expected or are dropping when soybeans are planted in the field. Lower yields will usually be associated with dryer growing seasons. Low levels of SCN may not produce visible aboveground symptoms, yet yields may be reduced. High SCN levels can cause plant stunting and yellowing. Aboveground symptoms can be confused with damage from compaction, nutrient deficiencies, drought stress, low-lying wet areas, herbicide injury, and other plant diseases. Circular to oval areas of stunted, yellowed plants can be observed. Areas of SCN injury are typically elongated in the direction of tillage practices, since the cysts are spread by tillage equipment.
For more information on Soybean Cyst Nematode visit http://cropwatch.unl.edu/plantdisease/soybean/soybean-cyst-nematode or contact your local extension office.