By Greg Tylka, Department of Plant Pathology and Microbiology
The soybean cyst nematode (SCN) remains a leading yield robber of soybeans in Iowa and much of the Midwest. The presence of SCN in the field may not be apparent by appearance of visual symptoms (aboveground stunting and/or yellowing) for years after the nematode is introduced in a field.
An easy way to check fields for the presence of SCN during the growing season is to look for telltale swollen, white SCN females on soybean roots. The SCN females are small, about the size of a period at the end of a sentence on a printed page. It takes four or more weeks after planting for the first SCN females to appear on roots in the spring.
Roots can be checked for presence of SCN now
In the first week of June, Tom Hillyer of Hillyer Agriservice, Inc. in West Liberty, Iowa, observed new, swollen SCN females on roots of soybeans that were planted on May 6. Newly emerged SCN females are considerably smaller and lighter in color than the root-colored nitrogen-fixing nodules.
Newly formed SCN females (black arrows) and nitrogen-fixing nodules (blue arrows) on soybean roots. Photo by Tom Hillyer.
To check soybean roots for SCN females, dig roots using a spade, then gently crumble away or shake off the soil to expose the roots for close observation. SCN females are visible to the unaided eye, but a magnifying glass or hand lens might help those without keen near vision. SCN females will be on soybean roots that are easy to dig from the soil through early August, but thereafter, the SCN females will form on new, fine roots that are difficult to reach by digging with a spade. So checking for SCN females on roots is best done over the next six to eight weeks.
More information about managing SCN
For more information about the biology and management of SCN, visit www.soybeancyst.info and www.soybeanresearchinfo.com/diseases/scn.html. Iowa State University's (ISU) management recommendations for SCN are available online in a downloadable format, Soybean Cyst Nematode (SCN) Management Recommendations, IPM 63. An annually updated list of SCN-resistant soybean varieties for 2014 is available in PDF format online at the ISU Extension and Outreach Online Store.
Greg Tylka is a professor with extension and research responsibilities in management of plant-parasitic nematode in the Department of Plant Pathology and Microbiology at Iowa State University. He can be reached at email@example.com or 515-294-3021.