The soybean cyst nematode (SCN) is a major pathogen of soybeans throughout Iowa, causing millions of dollars in yield loss each year. More than 70 percent of Iowa fields may be infested with the pathogen. The nematode has been found in every Iowa county except Adair, Adams, Allamakee, Clarke, Ida, Lucas, Lyon, Poweshiek, and Wayne. The nematode probably is present in these nine counties, but unfortunately, very few fields have been tested for SCN. SCN infestations often are not discovered until years after introduction of the pest because symptoms of SCN damage may not become readily apparent for many years. Proper soil sampling is important in early detection of the nematode. SCN can be detected in soil samples before obvious aboveground symptoms become apparent.

The Iowa State University (ISU) Plant Disease Clinic processed 4,335 soil samples from Iowa fields in 1998, 250 percent more samples than were processed in 1997. The number of samples submitted in 1998 was more than the total number of samples processed at ISU from 1993 to 1997. Samples were submitted for SCN testing from every Iowa county in 1998 except Adams, Clarke, Davis, Decatur, Dubuque, Lucas, and Wayne.

No SCN eggs were detected in 48 percent of the soil samples tested for SCN by the Plant Disease Clinic in 1998, and 28 percent of the samples had low SCN egg population densities (1 to 1,000 eggs per 100 cc or half-cup of soil). Moderate egg densities (1,001 to 5,000 eggs per 100 cc of soil) were discovered in 19 percent of the soil samples submitted last year. Only 5 percent of the samples processed in 1998 had SCN egg densities >5,000 eggs per 100 cc of soil. SCN was discovered in Ringgold, Taylor, Union, and Winneshiek counties for the first time in 1998.

SCN is a widespread and serious threat to soybean production in Iowa. Fortunately, soil sampling for this pest is easy, effective, and relatively inexpensive. Every field in which soybeans are grown in Iowa should be sampled for the presence of SCN. Fields can be tested in the spring prior to the planting of soybeans. Early detection of SCN infestations is an extremely important first step to effective, integrated management of SCN.

Additional information about SCN can be obtained from numerous ISU publications. Publication PD-32, Plant Nematode Sample Submission Form, is the form that should be submitted with soil samples to the ISU Plant Disease Clinic for SCN testing. This form also contains information on how to properly collect a soil sample for detection of SCN. Publication IPM-47s, Scouting for Soybean Cyst Nematode, illustrates the recommended procedures for scouting for SCN. The biology, life cycle, and recommended management of SCN are described in Pm-879, Soybean Cyst Nematode. Publication Pm-1649, Disease-resistant Soybean Varieties for Iowa, lists soybean varieties with resistance or tolerance to four major Iowa soybean diseases, including SCN. Single copies of each publication are available free of charge from county extension offices or from the Extension Distribution Center (515-294-5247).