By Greg Tylka, Department of Plant Pathology
A very quick and easy way to check for the soybean cyst nematode (SCN) is to dig roots and look for the presence of the telltale, swollen, white females on soybean roots. This technique is effective for checking fields for the presence of this serious yield-limiting pest and also for checking to see if SCN populations are building up on SCN-resistant soybean varieties. But checking roots in this manner can only be done during the growing season and only once females from the first generation of the season become apparent.
On Monday, June 20, I observed swollen, adult SCN females on roots of susceptible soybeans in Hamilton County and Franklin County, Iowa. The soybeans in Hamilton County were planted on May 18 near Williams and were in the V4 to V5 growth stage. Those in Franklin County, near Hampton, were planted on May 6 and were at V6 growth stage. The appearance of the SCN females indicates that growers and agribusiness personnel can begin checking fields for SCN.
White, adult SCN females on soybean roots.
Over the course of a week or two, the white, adult SCN females will turn yellow then tan, and eventually brown, as the female dies. And the brown, dead, egg-filled females (called cysts) will easily dislodge from the roots. But new, white adult SCN females will appear continuously throughout the growing season.
New SCN females appear on young soybean roots and those roots are deeper in the soil and farther laterally from the seed row later in the season (August and September) than in late June or early July. So one has to dig deeper as the season progresses in order to recover the young soybean roots on which new adult SCN females will appear.
The next four to six weeks (through July) are prime time to dig roots and check for SCN females.
Roots should not be pulled from the soil because the young roots with the SCN females attached will be stripped off. Roots should be dug with a shovel or spade and soil carefully removed from the roots.
Brown SCN cyst (dead female) on older soybean root.
Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes.