Damage due to the soybean cyst nematode (SCN) can reduce soybean yields in Iowa by 50 percent or more, particularly under very dry conditions. Yet, most of this yield loss can be prevented by growing SCN-resistant soybean varieties in fields known to harbor the nematode. There are hundreds of SCN-resistant soybean varieties available for Iowa growers to plant, and most seed companies do not charge extra for seed of these varieties. In addition to increased soybean yields, SCN-resistant soybean varieties prevent soil SCN population densities from increasing, thereby preserving the productivity of fields for future soybean production.
SCN often does not cause obvious symptoms to soybeans for many years after it becomes established in the field. Consequently, many fields in Iowa and surrounding states are infested with SCN unbeknownst to those who are farming the land.
Spring is a great time to sample fields to check for the presence of SCN. Soil samples should consist of 6- to 8-inch-deep soil cores collected from multiple locations within a defined sampling area within a field. Traditionally, this has meant collecting 20 soil cores in a zig-zag pattern from no more than 20 acres. The multiple soil cores should be mixed well in a bucket; then, a standard soil sample bag should be filled with the mixed soil.
Soil samples for SCN testing can be sent to the Plant Disease Clinic, 323 Bessey Hall, Iowa State University, Ames, IA 50011 or to a private soil testing laboratory that offers SCN sample analysis. The current fee for SCN analysis from the Plant Disease Clinic is $15 per sample for samples from Iowa; $20 per sample for out-of-state samples.
Several Iowa State University Extension publications on SCN can be obtained free of charge from any county extension office or on the Internet at www.soybeancyst.info.
Soil samples for testing for SCN should consist of multiple soil cores collected from throughout the sampling area. (Tom Schultz)
Healthy-looking soybeans infected with soybean cyst nematode at Field Extension Education Laboratory (FEEL) near Ames. (Greg Tylka)
This article originally appeared on page 58 of the IC-496 (4) -- March 13, 2006 issue.