The most yield-reducing pathogen of soybeans in Iowa is the soybean cyst nematode (SCN). It can decrease yields by 20 bushels per acre or more. The nematode survives over winter primarily as eggs in the soil. Juveniles hatch from eggs once soil temperatures reach 68 degrees F in the spring. They develop into new adult females 5 to 6 weeks after penetrating roots and beginning feeding. Once the first generation of SCN is completed, successive generations occur about every 28 days until soil temperatures drop below 68 degrees F in the fall.
Easily checking fields for SCN
Many SCN-infested fields go unnoticed because of subtle or absent above-ground symptoms, especially early in the growing season and also when SCN egg numbers are low or moderate. A quick and easy way to spot check fields for SCN is to look for SCN females on soybean roots. And now’s the best time to do that!
Dig (don’t pull) roots from the soil then gently shake the soil from the roots and look for small, white SCN females on the roots (see image below). The females are much lighter in color and smaller than nitrogen-fixing nodules, which are the same color as root tissue.
Farming with SCN
SCN is a chronic soybean health problem, not a death sentence for the crop. Other than identifying infested fields, not much can be done to manage SCN during the growing season. The time for active management begins in the fall after harvest and continues through the winter and up until spring when next year's crops are planted.
Fields in which SCN females are seen on soybean roots this year very likely will be planted to corn in 2026. Corn is not a host of SCN, so SCN egg numbers will not increase. In fact, SCN numbers will decrease in corn fields.
Many fields in which corn is grown in 2025 will be rotated to soybeans in 2026. These are the fields from which soil samples for SCN testing should be collected in the fall. Guidelines for collecting SCN soil samples will be reviewed in this blog later this year.
For all SCN-infested fields, farmers and those who advise them should spend time through the winter becoming familiar with the numerous nematode-protectant seed treatments and the hundreds of SCN-resistant soybean varieties that are available to combat SCN.
SCN management information available online
- annually updated ISU list of SCN-resistant soybean varieties for Iowa, ISU Extension publication CROP1649
- results of ISU evaluations of SCN-resistant soybean varieties throughout Iowa in 2024, ISU Extension publication IPM52
- annual results of ISU SCN-resistant soybean variety evaluations since 1997 (previous copies of ISU Extension publication IPM52)
- comprehensive information about SCN biology and management from the SCN Coalition
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on June 9, 2025. The information contained within may not be the most current and accurate depending on when it is accessed.
- Morrill Professor
- Nematologist
- Director of the Iowa Soybean Research Center