By Greg Tylka, Department of Plant Pathology
Many Iowa soybean fields may be infested with soybean cyst nematode (SCN) but the infestations may not be known because SCN does not always cause obvious, above ground symptoms. Up to 40 percent yield loss can occur without the appearance of above ground symptoms.
A free, easy and reliable way to check fields for the presence of SCN is to dig roots of susceptible soybean varieties, then carefully crumble away much of the soil from the roots and look for adult SCN females on the roots. The SCN females are small, round, white objects on the roots and are about the size of a period at the end of a sentence.
SCN females are present now on the roots of soybeans in Iowa. They will be apparent on young roots of susceptible soybean plants through July, August and probably early September.
It is easier to observe the nematode on soybean roots early in the season because the SCN females appear on new roots that can be easily dug from the soil surrounding the base of the stem of the plant. Later in the season, adult SCN females appear on new roots that are located deeper down in the soil and farther laterally from the stem of the plant.
SCN is spread by the movement of infested soil, so checking roots of plants near the entrance of fields where farm equipment enters and along fence lines where wind-blown soil accumulates may increase the likelihood of finding SCN-infected plants. Fields in which soybeans have been grown frequently in the past, and fields where soybean yields have declined over time for no apparent reason are logical places to start looking for SCN, too.
Additional information about the biology, sampling, and management of SCN can be found on the Web at www.soybeancyst.info/.
Adult SCN females (yellow arrows) on soybean root. The two larger round objects (orange arrows) are nitrogen-fixing nodules.
Areas of a field where SCN might be first discovered.
Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes. Tylka can be contacted at firstname.lastname@example.org or by calling (515) 294-3021.