Soybean cyst nematode (SCN) is a widespread and serious pest in Iowa soybean fields. An infestation can reduce yields by 50 percent or more. But surprisingly, fields can be infested with the nematode for years without noticeable symptoms.
Greg Tylka, Iowa State University nematologist, said the only consistent and reliable sign of an SCN infestation is the presence of adult SCN females and cysts (dead females) on the roots of infected soybean plants.
"These adult SCN females and cysts are small, round, white- to yellow-colored objects that can be seen on infected soybean roots with the unaided eye. They are about the size of a period at the end of a sentence," Tylka said.
"It takes four to six weeks for the first SCN females to appear on the roots of a new soybean crop. We are just now seeing females on roots of soybeans planted in Ames on May 10," he said.
SCN females and cysts will be on roots of infected plants through much of the growing season, until late summer or early fall when the plants begin to mature. But Tylka said it is easier to see the nematode on soybean roots early in the season because the females and cysts appear on new roots that can be easily dug from the soil. "Later in the season, adult SCN females and cysts appear on new roots that are located deeper in the soil as well as farther laterally from the stem of the plant," he said.
Once SCN infestations are found in fields, SCN-resistant soybean varieties can be grown in future years to prevent build up of the nematode and to boost soybean yields. But Tylka said the first step is to figure out if SCN is present before the pest can be managed properly.
Iowa State University publication IPM-47s, "Scouting for Soybean Cyst Nematode," illustrates the recommended procedures for SCN scouting. Single copies are available free of charge from county extension offices or from the Extension Distribution Center (515) 294-5247. Additional information about SCN can be found on the Web at: www.soybeancyst.info  .