The first generation of soybean cyst nematode (SCN) females is now visible on the roots of soybeans growing in SCN-infested fields in Iowa. The SCN females, which contain 250 or more eggs each, are white and about the size of a period at the end of a printed sentence (see photo above). The females are much smaller and lighter in color than nitrogen-fixing nodules, which are the color of the roots.
Unfortunately, resistance-breaking populations of SCN are somewhat common in Iowa and throughout the Midwest these days. Checking the roots of SCN-resistant soybean cultivars for SCN females is a good way to gauge if the resistant cultivars are not controlling the nematode. Seeing a few SCN females on the roots of a resistant soybean plant would not be cause for great concern.
Dig and look at roots from multiple places throughout various parts of the field. If SCN hasn’t been found in a field previously, high-risk areas for initial infestation of fields include near the field entryway, in low spots, and along fence lines where windblown soil accumulates (see diagram).