By Greg Tylka, Department of Plant Pathology
Research and extension personnel in Iowa have tracked soybean cyst nematode (SCN) infestations by county since initial discovery of the nematode in Winnebago County in 1978.
This map indicates the years that counties were Infested with soybean cyst nematode.
SCN was discovered for the first time in many different Iowa counties in the 1980s and 1990s. But by 2000, there were only nine Iowa counties in which SCN had not yet been found. The nematode was discovered in a few new Iowa counties from 2000 to 2006, but, it had still not yet been found, or at least officially confirmed, in three Iowa counties – Allamakee, Ida, and Lyon Counties – by the end of 2007.
ISU Extension field agronomist Joel DeJong conducted a survey for SCN in several counties in the northwest corner of Iowa in 2007, including Lyon County. The survey was supported by the ISU Corn and Soybean Initiative and soybean checkoff funds from the Iowa Soybean Association.
SCN had informally been known to be present in Lyon County for a few years, and cyst nematode eggs were recovered by private laboratories from soil samples taken from Lyon County in the past. But SCN had never been officially confirmed by greenhouse testing.
Eggs believed to be from SCN were recovered from soil samples collected as part of the survey from two fields in Lyon County in 2007. To confirm that the sampled fields were infested with SCN and not some other cyst nematode, follow-up soil samples were collected from the Lyon County fields early in 2008, and susceptible soybeans were grown in the soil samples in a greenhouse for a month. Many SCN females were observed on the soybean roots, confirming the presence of SCN in the county.
Iowa counties (in red) infested with soybean cyst nematode as of June 2008.
There now are only two Iowa counties in which there is no official record of SCN – Allamakee and Ida County. If anyone knows of SCN in fields in either Allamakee or Ida County, they are encouraged to send soil samples from the fields to the Plant and Insect Diagnostic Clinic, 327 Bessey Hall, Iowa State University, Ames, Iowa 50011, so that soybeans can be grown in the soil to verify the presence of SCN.
Although SCN has been found in almost every Iowa county, every field in the state is not infested with the nematode. A comprehensive survey of Iowa currently is being conducted by ISU personnel in collaboration with the USDA National Agricultural Statistics Service (NASS) personnel and supported by soybean checkoff funding from the Iowa Soybean Association.
In 2007, soil samples were collected from 205 randomly selected fields, and the nematode was found in 71 percent of the fields. This survey will continue through 2008 and 2009. A summary of the 2007 survey findings is available.
Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes.