By Greg Tylka, Department of Plant Pathology and Microbiology
The soybean cyst nematode (SCN) is one of the most serious soil-borne pathogens of soybean in Iowa and throughout the Midwest. 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 (Figure 1). 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.
Figure 1. Hatched SCN juveniles (stained purple) penetrating soybean root on way to vascular tissue for feeding.
Soybean cyst nematode females are round, white, and large enough to see with the unaided eye (Figure 2). 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.
Figure 2. Swollen, white SCN females visible on soybean roots with the unaided eye.
The first generation of adult SCN females are appearing now. 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 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 to check 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.
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.
More information about the biology and management of SCN can be found at www.soybeancyst.info.
Greg Tylka is a professor with extension and research responsibilities in management of plant-parasitic nematode in the Department of Plant Pathology and Microbiology at Iowa State University. He can be reached at email@example.com or 515-294-3021.