Now is the time to look for soybean cyst nematode females on soybean roots in fields. "The soybean cyst nematode, or SCN, continues to cause serious soybean yield losses in Iowa and throughout the Midwest," says Greg Tylka, an Iowa State University Extension nematologist. "It is easy to identify SCN infestations in the field during the growing season by checking soybean roots for the presence of SCN females." In the following article, Tylka discusses the benefits of checking soybean roots in fields that are planted with susceptible soybean varieties and also why you should check SCN-resistant soybean varieties, too.
SCN is one of the most serious robbers of soybean yields in Iowa and Midwest
The soybean cyst nematode is one of the most serious soilborne pathogens of soybean in Iowa and throughout the Midwest, he says. Juveniles of this microscopic worm hatch from eggs in the spring, then burrow into soybean roots, where they attach to the vascular tissue of the plant and feed (see photo). Developing SCN females get progressively larger as they mature, until their fully expanded, lemon-shaped bodies rupture out of the root and become visible on the root surface.
Soybean cyst nematode females are round, white and large enough to see with the unaided eye (see accompanying photo). It takes four to six weeks or more for the first SCN females of the season to develop sufficiently to rupture out of and become apparent on the surface of soybean roots, says Tylka.
The first generation of adult SCN females are appearing now—the first and second weeks of June. So the next six to eight weeks (through July) are prime time to dig roots and check for SCN females in Iowa. Plants should not be pulled from the soil, says Tylka. That's because the young roots with the SCN females attached will be stripped off. Instead, roots should be dug with a shovel or spade, and soil should be carefully removed from the roots.
Two reasons why you should check soybean roots for SCN females
"Observing SCN females on roots of susceptible soybean varieties is a quick and easy way to check the presence of this pathogen in a field, which is the first step towards successful management of SCN," says Tylka.
"Also, checking the roots of resistant soybeans for SCN females in fields that are infested is a good way to monitor the effectiveness of the resistant varieties," he adds. More information about the biology and management of SCN can be found at www.soybeancyst.info.