As the 2026 soybean harvest wraps up across Indiana, growers have an excellent opportunity to assess one of the most damaging and often overlooked threats to soybean production: soybean cyst nematode (SCN, Heterodera glycines). SCN is the leading yield-limiting pathogen of soybean in the United States, causing an estimated $1.5 billion in annual losses.
One of the biggest challenges in managing SCN is that infected soybean plants may appear healthy even when significant yield losses are occurring. If your corn yields have been steadily increasing while soybean yields remain stagnant, SCN could be one of the contributing factors. Even if you have never observed symptoms of SCN in your fields, that does not mean the nematode is absent. Fall soil sampling is a simple and effective way to determine whether SCN is present and assess its population density.
Why Should Indiana Growers Be Concerned About SCN?
SCN is widespread in Indiana soybean fields. Growing SCN-resistant soybean varieties has been the primary management strategy for decades. However, approximately 95% of commercially available SCN-resistant varieties rely on the same resistance source, PI 88788. Repeated use of this resistance source has allowed SCN populations that can overcome PI 88788 resistance to become more common, reducing the effectiveness of these resistant varieties. Regular soil testing is essential for monitoring SCN population densities and evaluating whether current management practices are effectively suppressing the nematode.
Why Is Fall a Good Time to Sample for SCN?
Fall, particularly after soybean harvest, is a convenient time to collect soil samples for SCN testing. SCN populations can increase substantially throughout the soybean growing season, and population densities are often highest near crop maturity or shortly after harvest. Sampling at this time provides an opportunity to assess SCN population levels following the growing season. Fall sampling also gives growers sufficient time to review their SCN test results and make informed management decisions before the next soybean crop.
How to Collect Soil Samples for SCN Testing
Collecting soil samples for SCN is relatively simple and can often be incorporated into routine soil sampling activities. SCN populations are often unevenly distributed within fields, so collecting multiple soil cores is important for obtaining representative results. The SCN Coalition recommends the following practices:
- Collect 15–20 soil cores from an area of approximately 20 acres. Sample smaller areas separately when soil types, cropping histories, or field conditions differ.
- Sample 6–8 inches deep using a soil probe or shovel.
- Follow a zigzag or W-shaped pattern to collect cores across the sampling area.
- Combine and thoroughly mix the soil cores in a clean bucket, then place approximately 2 cups of soil into a labeled plastic bag.
- Keep samples cool and out of direct sunlight until they can be delivered to a diagnostic laboratory.
Several university diagnostic laboratories in the Midwest provide soil testing services for soybean cyst nematode. More information of soil test labs can be found at the SCN Coalition website. When requesting testing, specify that an SCN egg count is needed to assess nematode population density.
- University of Missouri – SCN Diagnostics
- Location: Columbia, Missouri
- Phone: 573-884-9118
- Email: scndiagnostics@missouri.edu
- Website: https://scndiagnostics.com/soil_testing/
- University of Illinois – Plant Clinic
- Location: Urbana, Illinois
- Phone: 217-333-0519
- Email: plantclinic@illinois.edu
- Website: https://extension.illinois.edu/plant-clinic
SCN Testing Cost: Routine SCN soil testing generally costs approximately $25–$50 per sample, depending on the laboratory. Growers are encouraged to check with their preferred laboratory for current pricing and sample submission instructions.
Know Your SCN Numbers and Plan Ahead
Soil testing provides valuable information about SCN presence and population density. Growers can use these results to make informed management decisions, including rotating to non-host crops such as corn and selecting soybean varieties with different sources of SCN resistance. Information on commercially available SCN-resistant soybean varieties, including their resistance sources, can be found in the 2027 Illinois Soybean Variety Guide. If your preferred seed brand is not included in the guide, contact your seed dealer or company representative for information about available SCN-resistant soybean varieties and their resistance sources.
Links:
- Scouting and soil testing for SCN: https://www.thescncoalition.com/wp-content/uploads/2021/12/Scouting-and-Soil-Testing-for-SCN-Resource.pdf
- SCN soil testing labs: https://www.thescncoalition.com/state-information/soil-testing-labs/
- 2027 Illinois Soybean Variety Guide: https://publish.illinois.edu/freescntesting/files/2026/10/Illinois-2027-soybean-varieties-flier.pdf
