The soybean cyst nematode (SCN) is widespread throughout Iowa and surrounding states, and as much as 40% yield loss can occur from SCN damage without symptoms appearing on the soybean plants. Symptoms typically are not apparent when temperatures are moderate and rainfall is adequate to excessive during the growing season. The following information is provided by Greg Tylka, Iowa State University Extension plant pathologist and nematologist.

Symptoms generally begin to appear starting in mid-July and last through most of the growing season. Symptoms of SCN damage include stunting of plants, yellowing of foliage (not just leaf margins or areas between leaf veins) and mid-day wilting.

The only way to check for SCN in the field is to dig roots, gently remove soil from the roots, and look for the egg-filled, round, white SCN females on the roots. The females are about the size of the head of a straight pin or a period at the end of a sentence in a newspaper or magazine, and for most people, the females can be seen with the unaided eye.

The first SCN females of the 2010 growing season appeared several weeks ago (June 7, 2010 Integrated Crop Management News),  and SCN females should be apparent on infected roots through August.

Dig some plants now and carefully look at the soybean roots

Carefully observing soybean roots for SCN females is a good way to check fields for infestations that have not yet been discovered. It also is effective to assess how well SCN-resistant soybean varieties are controlling nematode reproduction in fields known to be infested with SCN. There should be only a few, say 10 to 20, SCN females on the roots of a resistant soybean variety if the variety is effectively controlling the nematode.