Source: Iowa State University
The soybean cyst nematode (SCN) is widespread throughout Iowa and surrounding states, and as much as 40 percent yield loss can occur from SCN damage without symptoms appearing. Symptoms typically are not apparent when temperatures are moderate and rainfall is adequate to excessive during the growing season.
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.