Soybean cyst nematode, Heterodera glycines, is a small, unsegmented plant-parasitic roundworm that attacks the roots of soybeans. Many plant-parasitic nematodes are believed to be endemic or native to the United States, but soybean cyst nematode likely was introduced from Japan. Soybean cyst nematode was first discovered in the United States in 1954 in North Carolina (Winstead et al., 1955), and since has spread to 27 additional -states in the Southeast and Midwest (Noel, 1992). It was first discovered in Iowa in Winnebago County in 1978. In 1996, soybean cyst nematode was identified for the first time in Grundy, Mahaska, and Ringgold Counties. Currently, the nematode is known to exist in 72 Iowa counties and is suspected to be present in many other counties as well.