According to several surveys, the soybean cyst nematode is the most significant soil-borne pathogen of soybean. In a heavily infested field, the nematode can cause more than 30% yield loss and as much as 100% in some sandy soils with dry weather conditions. Farmers often underestimate yield loss caused by the nematode because yield losses could occur without obvious above-ground symptoms.

Symptoms of SCN infections can range from no visible evidence of plant injury to plant death in certain areas of the field. The symptoms commonly associated with SCN damage are similar to other crop production problems such as potassium and nitrogen deficiencies, iron chlorosis, herbicide injury, soil compaction, drought stress, and other soybean diseases. In high-yield production fields (greater than 40 bushels/acre) or during years when soil moisture from rainfall or irrigation is plentiful, visible symptoms of SCN damage are rarely seen. Research has shown, however, that yield losses of 15 to 30% 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 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

SCN females have begun to be observed on the roots of soybean this season. Consequently, for central and southcentral MN, now is the time to begin scouting fields for SCN by checking soybean roots for females and cysts. 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.

To scout for SCN in fields where the nematode has not yet been found, you may target fields in which soybean has been grown frequently in the past and fields where soybean yields have declined over time for no apparent reason. SCN is more prevalent in greater numbers in areas of fields with high pH (greater than 7.5). Because SCN is spread by the movement of infested soil, checking roots of plants near the entrance of fields where farm equipment enters and along fence lines where windblown soil accumulates also may increase the likelihood of finding SCN-infected plants.

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. Soil samples should be submitted to commercial soil testing laboratories or the University of Minnesota Nematology lab as follows:

• Collect a core or ¼ cup from 20 different locations within an area no larger than 10 acres in order to reduce variability of testing results.
• Sample the area in a zigzag pattern. Collect soil at a depth from zero to eight inches. In soybeans, take from the root zone (not between the rows). If possible the use of GPS coordinates at each of the sampling sites can allow for better monitoring of nematode populations.
• Do not collect the sample from the center of the affected area because these plants usually have severely stunted root systems that cannot support SCN. This will result in low numbers, when in fact the field may have higher numbers on average.
• Send one pint of soil from mixed sub-samples in plastic or paper soil test bags. If the samples will not be sent to the lab immediately, then place them in the refrigerator or freezer until ready to ship so the eggs don’t hatch.

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 from the SROC Website (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.

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