E-210
DEPARTMENT OF ENTOMOLOGY
field crop insects

SOYBEAN CYST NEMATODE
John M. Ferris, Extension Nematologist, and C. Richard Edwards, Extension Entomologist

Soybean cyst nematode (SCN) has become a severe problem in Indiana, partly because of the state’s intensive soybean culture. This nematode has caused marked yield losses (up to 50%) in over 30 counties in the state.
Symptoms of SCN injury can easily be confused with other problems such as nutrient deficiencies, herbicide injury, disease, poor drainage, etc. The presence of oblong areas of stunted, yellowed plants extending in the direction of tillage is suggestive of SCN damage. The damage may also be recognized as a failure of the canopy to close. Symptoms are generally more pronounced when soybean plants are under stress from such conditions as drought, low fertility, or compaction. Infected plants have poorly developed roots and very few Rhizobium nodules. Close examination of the roots may also reveal extremely small, white to yellow spheres (bodies of female nematodes) attached to the root surface. These females are not much bigger than grains of coarse sugar, and should not be confused with the much larger Rhizobium nodules.

BIOLOGY AND LIFE CYCLE
This nematode, like all nematode species, is an unsegmented roundworm. Stages in the life cycle include egg, juvenile (larva), and adult. The infective stage of the nematode is a wormlike juvenile which hatches from an egg and moves a short distance through the soil until it encounters a soybean root. The juvenile enters the root, begins to feed, and eventually grows (by a series of molts) into a lemon-shaped adult female which may contain 200-500 eggs. At this stage the nematode is loosely attached to the root by the head and neck, with the swollen portion of the body protruding from the root surface. When the female dies, the cuticle turns brown and becomes a tough, protective package for these eggs. This stage, called a cyst, is very resistant to decay
and can remain in the soil many years while containing viable eggs ready to hatch whenever soybeans are grown.
The life cycle of SCN, from egg to egg, takes 21 -25 days under optimum conditions (soil temperature 24-28°C, 75-82°F); thus several generations are possible during each growing season.

RACES
In the scientific literature, at least five races of SCN have been identified. These races are defined by their ability to reproduce on four standard differentials (varieties and inbreds). However, classification of races in this fashion can be misleading. For example, when just one other differential is added to the screening process, Races 3 and 4 are each split in two, resulting in four "races" of these two races. We have found that nematode populations from different areas of Indiana seem to have a greater amount of variability than would be indicated by the simple five-race concept. Recognition of these population differences may explain why a variety, supposedly resistant to Race 3, may actually suffer yield loss when grown in afield with "Indiana Race 3." Thus, we feel that the current race concept does not have much practical application.

SAMPLING FOR SCN
If the pattern of poor soybean growth in a field suggests nematode injury, soil and root samples should be collected and sent to a nematology laboratory for analysis. It is often desirable to collect two separate samples. One should be from an area in which plants are growing unsatisfactorily. A second should be taken from an area of the field in which plants appear to be growing in a more normal, healthy fashion. Place each sample, consisting of approximately a quart of soil plus roots, in a plastic bag and close with a rubber band or string-tie.

PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, IN 47907