The soybean cyst nematode (SCN) first appeared in the United States in North Carolina during the 1950s. In Iowa it was first discovered in Winnebago County in 1978. SCN is spreading rapidly; it has since been identified in over half of the counties in the state (see Fig. 1). In Winnebago County alone, soybean yield losses from SCN have cost growers nearly $2 million per year. Of the more than 2,000 soil samples from around the state that were tested for SCN by the Iowa State University Cooperative Extension Service in 1988, more than 75% were found to be infested. In fact, a majority of the samples contained SCN densities greater than 1,000 eggs per 100 cubic centimeters of soil. Significant yield suppression has occurred in Iowa at densities much lower than this. In short, SCN is rapidly becoming a major factor in limiting soybean yields through Iowa.
Available at: http://works.bepress.com/george_kraus/10/