More than 100 fields throughout Iowa were surveyed for the presence of the soybean cyst nematode (SCN) in 2016 in a project sponsored by the ISU Soybean Research Center and the Iowa Soybean Association (ISA). Soil samples were collected by Iowa State University Extension and Outreach field agronomists and ISA staff and interns and sent to the ISU Plant and Insect Diagnostic Clinic for processing.
Low egg counts (50 and 100 eggs per 100 cc soil) were found in samples collected from a field in Allamakee County by ISU Extension and Outreach field agronomist Brian Lang for the project. These results were significant because SCN had been officially confirmed in every county in Iowa except Allamakee County.
Low SCN egg counts such as these often can be the result of a stray nematode egg or two in sample processing (i.e. a false positive result). So it was necessary to confirm that the samples were infested with SCN by growing susceptible soybeans for 30 days in soil collected from the field and then carefully examining the roots of the plants for the presence of newly formed, white SCN females (see figure).
A total of 14 SCN females were observed on roots of 12 different soybean plants growing in the soil collected from the field in Allamakee County. This finding represents the first discovery of SCN in Allamakee County and confirms the presence of SCN in the last of Iowa’s 99 counties.
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