Soybean cyst nematode (SCN) is a widespread and serious pest of soybeans in Iowa. But the nematode often does not cause obvious above-ground symptoms, at least not until population densities become extremely high. One fairly consistent, albeit somewhat indirect, symptom of SCN parasitism that is apparent at this time of the year is early senescence of the soybeans. The early senescence of soybean caused by SCN is illustrated in the diagram on page 227. The squares in the map in the diagram represent 3-foot by 3-foot (9 ft2) square areas of the field. Three 1-inch diameter, 8-inch deep soil cores were taken from each square in May.