Soybean Cyst Nematode - Life Cycle

The SCN life cycle has three major stages: egg, juvenile, and adult. The life cycle can be completed in 24 to 30 days under optimum conditions.

Figure 1. Cysts of the soybean cyst nematode.
Photo © Terry Niblack, University of Illinois

Figure 2. Lemon-shaped cysts on roots.
Photo © Greg Tylka, Iowa State University Click on imge to view larger version

  1. Cysts of varying shades of brown contain eggs of the nematode (Figure 1). Cysts survive in soil for many years. The number of cysts in a soil test is a good indication of SCN population in that soil.
  2. When temperature and moisture levels are favorable in the spring, worm-shaped juveniles hatch from eggs in the soil. These juveniles are the only life stage of the nematode that can infect soybean roots. This juvenile stage can also be detected in soil tests, but is a less reliable indicator of nematode populations than the cysts.
  3. Juveniles move through the root until they contact vascular tissue. There they start to feed. As the nematodes feed, they swell and eventually female nematodes become so large that they break through the root tissue and are exposed on the surface of the root. Plant damage is due mainly to this stage of the SCN life cycle.
  4. Some eggs are produced on the outside of the female's body. These eggs hatch and young juveniles reinfect the plant root. Up to 3-4 generations can occur over a single growing season .
  5. Other eggs remain in the female's body and as it matures and dies, the body becomes a cyst, a protective case that can sometimes be seen on plant roots (Figure 2), and which can survive in soil for many years. The cysts are about the size of a pinhead and are much smaller than nitrogen nodules.
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