July 2, 2003
AMES, Iowa — At this time of the growing season the soybean cyst nematode (SCN), a widespread and serious pest of soybeans throughout Iowa, is easy to find on roots.
"It takes about four to six weeks for the first SCN females to appear on the roots of the new soybean crop," said Greg Tylka, Iowa State University nematologist. "We are just now seeing females show up on roots of soybeans planted in Iowa during the last 10 days of May."
Adult SCN females and cysts are small, round, white to yellow objects that can be seen on infected soybean roots with the unaided eye. They are approximately the size of a period at the end of a sentence.
Although SCN is capable of reducing yields by 50 percent or more, it can infest fields for years without noticeable symptoms. Tylka said the only consistent and reliable sign of SCN in a field is the presence of adult females and cysts (dead females) on the roots of infected soybean plants.
The 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 soybeans begin to mature, Tylka said, but now new roots can be easily dug from the soil. Later in the season, the adult SCN females and cysts are on roots that are located deeper in the soil and farther away from the stem of the plant.
If females or cysts are found, that knowledge can be used to deal with the pest. Tylka said SCN-resistant soybean varieties can be grown in future years to prevent build up of the nematode and to boost soybean yields.
"You have to first know that SCN is present in your fields before you can begin managing it properly," he added.
Additional information about SCN can be found on the web at www.soybeancyst.info.