Iowa’s early planting season means pests like the soybean cyst nematode are off to a quick start this year, which could result in a greater risk of severe damage from SCN throughout the growing season. This nematode is a major yield-reducing pathogen of soybeans and is widespread across Iowa and other Midwest states. Research conducted in recent years indicates that many fields have not been checked for SCN. 

Iowa State University Extension nematologist Greg Tylka offers the following recommendation for a quick and economical way to check for the presence of this yield-robbing pest in a field. 

One of the easiest and cheapest ways to check a field for the presence of SCN is to dig soybean roots with a spade, shake the soil from the roots, and look for small, white, round objects on the roots. These objects are SCN females, and each one contains 200 or more eggs. SCN females are much smaller and lighter in color than the nitrogen-fixing nodules that form on healthy soybean roots. 

 
WHAT TO LOOK FOR: This soybean root has the cysts that are white SCN females (yellow arrows) and the larger nitrogen-fixing nodules (blue arrows). 

“Checking soybean roots in this manner also is a quick and easy way to gauge whether a resistant variety is effectively controlling SCN,” Tylka says. Only a few SCN females should be seen on the roots if the resistance trait in a soybean variety is working effectively. But if the SCN population present in a field has built up virulence on the resistance genes in the soybean variety, there will be many SCN females present on the roots of the plants. 

SCN is visible on soybean roots dug through mid-August. The SCN females fade from white to yellow, then become tan and eventually brown within a few days to a week as the female dies and the body wall hardens to form a cyst around the eggs within the cyst.

It is almost impossible to see brown SCN cysts on soybean roots dug from a field with the unaided eye. Some white adult females should be apparent on roots of soybeans growing in SCN-infested soil no matter when the roots are dug. 

Fields can be checked for SCN by carefully digging and observing roots through June, July and into mid-August, Tylka says. In warm summer soils, SCN can complete a generation in four weeks, ending with formation of new females on roots. The newly formed SCN females occur on younger roots and as the season progresses, those new roots are forming deeper in the soil and farther from the stem of the plant. Therefore, it is advised to dig deeper for roots in July and August to look for SCN females. 

To learn more about SCN biology, management and testing of soil samples for this pest, soybean farmers have several sources. Information is available online explaining the biology and management of SCN and guidelines on how to scout fields for SCN.  

“You need to properly collect and submit soil samples to the lab for testing,” Tylka says. For this information, he suggests you check out these three websites:

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