Soybean cyst nematode (SCN) is an important, widespread soybean pest in Iowa that often goes unnoticed. To date, the nematode has been discovered in all but five Iowa counties. The only consistent and reliable sign of an SCN infestation in the field is the presence of adult SCN females and cysts (dead females) on the roots of infected soybean plants. Adult SCN females and cysts are small, round, and white to yellow, each approximately the size of a period at the end of a sentence.
SCN females are beginning to appear on the roots of soybean in research plots that were planted May 10 in Ames. Consequently, now is the time to begin scouting fields for SCN by checking soybean roots for females and cysts. You will be able to see females and cysts on roots of infected plants through much of the growing season, until late summer or early fall when the plants begin to mature. It is easier to observe the nematode on soybean roots early in the season because the females and cysts occur 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 appear on new roots that are located deeper down in the soil as well as farther laterally from the stem of the plant.
|Adult soybean cyst nematode females on soybean roots.|
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.
|Digging roots for soybean cyst nematode.|
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 wind-blown soil accumulates also may increase the likelihood of finding SCN-infected plants.
Collection of 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 a private soil testing laboratory that offers nematode testing or to the ISU Plant Disease Clinic for extraction and counting of SCN eggs. Samples sent to the ISU Plant Disease Clinic should be accompanied by a completed Plant Nematode Sample Submission Form (ISU Extension publication PD 32), and there currently is a $15 per sample charge for processing each sample. Detailed instructions on how to collect a representative soil sample for detection of SCN can be found on the back of PD 32.
Iowa State University Extension publication IPM 47s, Scouting for Soybean Cyst Nematode , illustrates the recommended procedures for scouting for SCN. Single copies of this publication are available free of charge from county extension offices or from the Extension Distribution Center by calling (515) 294-5247. Additional information about SCN can be found on the Web at www.soybeancyst.info
This article originally appeared on page 103 of the IC-488(13) -- June 17, 2002 issue.