Soybean cyst nematode, Heterodera glycines, is a small, unsegmented plant-parasitic roundworm that attacks the roots of soybeans. While many plant-parasitic nematodes are believed to be endemic or native to the United States, soybean cyst nematode is believed to have been introduced from Japan. Soybean cyst nematode was first discovered in the United States in 1954 in North Carolina (Winstead et al., 1955), and has since spread to 25 additional states in the Southeast and Midwest (Noel, 1992). It was first discovered in Iowa in Winnebago County in 1978. In 1994, soybean cyst nematode was identified for the first time in Carroll, Davis, Henry, and Sac Counties. Currently, the nematode is known to exist in 62 Iowa counties (Figure 1) and is suspected to be present in other counties as well.