In a field heavily infested with the soybean cyst nematode (SCN), the nematode can cause more than 30 percent yield loss; even 100 percent in some sandy soils with dry weather conditions.

Fortunately, SCN has not become widely established in the region, currently being limited to fields in Traverse, Grant, Stevens and counties southward in Minnesota; Richland County, North Dakota; and Roberts County, South Dakota (Figure 1). Because of the close establishment in neighboring counties, growers and ag industry reps should become aware of symptoms, check roots, and maintain their vigilance.

Symptoms of SCN infections can range: all the way from no visible evidence of plant injury to plant death in certain areas of the field. The symptoms commonly associated with SCN damage resemble other crop production problems such as potassium and nitrogen deficiencies, iron chlorosis, herbicide injury, soil compaction, drought stress and other soybean diseases (Figure 2).

You rarely see symptoms of SCN in high-yield production fields (greater than 40 bushels/acre) or during years when soil moisture from rainfall or irrigation is plentiful.  Research has shown, however, that yield losses of 15 to 30 percent on a susceptible variety are common in these fields. Soybean farmers in these situations often notice poor or no longer increasing yields over several years, uneven plant height in the field, a delay in canopy closure, or early senescence.

Scouting for females on soybean roots (Figure 3) is a convenient way to detect nematode infestation in a field. Root samples may be taken at any time from five weeks after planting through late season. In Minnesota, the best time to scout for females on the roots, however, is early July when females of the first generation become white to yellow and are exposed to the outside of roots.

When the plants are carefully dug with a shovel and the soil is gently removed from the roots, most females stay on the roots. These females are lemon-shaped and about 1/40 inch long and 1/60 inch wide and can be seen by the naked eye
These females and cysts will be apparent on roots of infected plants until late summer or early fall, when the plants begin to mature. However, it is much easier to observe the nematodes on soybean roots in the first half of the season because they form on new roots that can be easily dug from the soil surrounding the base of the stem of the plant. Later in the season, adult SCN females and cysts occur on new roots that form deeper in the soil as well as farther laterally from the stem of the plant.

Collecting soil samples from fields suspected of being infested with SCN is an alternative to digging soybean roots and looking for adult females and cysts. Soil sampling can be done at any time during the growing season.
SCN testing labs in south central and central Minnesota include the University of Minnesota Nematology Lab, Southern Research and Outreach Center, Waseca, (507) 837-5649.

Submission forms can be downloaded at:

http://sroc.coafes.umn.edu/Nematology/Cyst%20Soil%
20Sample%20Form.pdf 

There is a $20 fee per submitted soil sample.

Commercial labs include AGVISE Laboratories, Benson, (320) 843-4109; and MVTL Laboratories, New Ulm, (800) 782-3557.

For more details, including directions on how to collect and submit samples for SCN testing, see Minnesota Crop eNews, published by the U of MN Extension Service. You’ll find it at:

http://www.extension.umn.edu/cropenews  

Dave Nicolai Regional Educator - Crops
U of MN Extension Service Regional Center, Hutchinson