The soybean cyst nematode (SCN) is present in many fields throughout Iowa and surrounding states, and the nematode can reduce soybean yields significantly. Fields may not exhibit stunting and foliar chlorosis due to SCN feeding in seasons of adequate to excess moisture. Fall is the optimum time to sample fields for SCN.
Soil sample results collected from fields where soybeans were grown in 2025 will reveal how SCN might have affected soybean yields. For fields in which corn was grown in 2025 but soybeans will be grown in 2026, fall soil sample results will indicate if SCN is present and, if so, what levels “lay in wait” for next year’s soybean crop.
How to collect an SCN soil sample
The procedure for collecting SCN soil samples from harvested soybean or corn fields in the fall is listed below.
- Use a soil probe, not a spade, to collect soil cores.
- Soil cores should be collected from the surface to eight inches deep.
- Collect 15 to 20 soil cores from every 20 acres.
- Collect soil cores from similar management zones in the field, if present (see figure below), or in a zig-zag pattern.
- Combine all soil cores from a sampled area in a bucket, mix the soil well, and fill a labeled soil sample bag or plastic bag.
- SCN soil samples need not be refrigerated; storing them at room temperature is sufficient.
- The ISU Plant and Insect Diagnostic Clinic processes SCN soil samples for farmers and agronomists. Samples can be delivered or mailed to room 2445 Advanced Teaching and Research Building, 2213 Pammel Drive, Iowa State University, Ames, IA 50011. The clinic can be contacted by calling 515-294-0581 or by emailing pidc@iastate.edu. More information is available online, and the Plant and Insect Diagnostic Clinic Nematode Sample Submission Form can be downloaded from the ISU Extension Store.
- There are private soil-testing labs that process soil samples for SCN, too. The SCN Coalition has a list of such facilities online.
What are the steps for managing SCN in fields where it is detected?
Managing SCN requires an active, multiple-prong approach. Farmers should grow SCN-resistant soybean varieties with PI 88788 and with Peking resistance in alternating soybean crops and in annual rotation with corn, which is an SCN nonhost. Also, there are nematode-protectant soybean seed treatments that may provide added yield protection. A wealth of information about actively managing SCN is available on the SCN Coalition website.
Using soil sample results to estimate yield loss from SCN in a field
Potential yield loss from SCN can be estimated for individual fields by using the SCN Coalition’s Profit Checker. The Profit Checker uses results of analyses of data from >35,000 Iowa State University SCN-resistant soybean variety trial research plots in experiments conducted in all nine crop-reporting districts of the state over more than 20 years.
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- Morrill Professor
- Nematologist
- Director of the Iowa Soybean Research Center