Managing Soybean Cyst Nematode - Facts, Stages and Symptoms

By Steve Butzen, Agronomy Information Specialist

Key Facts

 

  • Soybean cyst nematode (SCN) is the single most damaging pest of soybeans in the United States.
  • SCN may decrease yields substantially without inducing obvious symptoms. Consequently, many fields are infested without the knowledge of the grower.

    SCN may cause substantial yield loss without inducing obvious symptoms.

  • It takes a period of years for SCN to build up in fields to damaging levels. Preventing this buildup requires early detection and management. Sampling fields with no symptoms is the only way to detect SCN before it becomes an economic problem.
  • SCN requires a combination of management strategies for effective control. In addition to prevention, rotation and planting SCN-resistant varieties, any practice which promotes good soybean health and growth will also help against SCN.
  • SCN cannot be eradicated once it infests a field, which makes its rapid spread to new fields especially troublesome.

 

SCN may cause substantial yield loss without inducing obvious symptoms.

SCN Stages

Photo: SCN adult female cyst
SCN adult female cyst

SCN is a tiny worm-like parasite with a three-stage life cycle: egg, juvenile and adult. Juveniles, the only stage that can infect the plant, are capable of moving only a short distance through the soil as they search for a host plant. Upon finding one, they burrow into the plant root and begin to feed on young root cells.

SCN Damage/Symptoms

Feeding Damage - SCN damages soybean plants in various ways:

Above-Ground Symptoms - SCN infestations can result in circular or oval-shaped patterns of yellow, stunted, less vigorous plants. Often, there is a sharp dividing line between affected and non-affected areas of the field. In the affected areas, rows are slow to close and may remain so throughout the season. These symptoms, however, are not unique to SCN, and could also be caused by compaction, herbicide injury, drought stress, other plant diseases, iron deficiency chlorosis or another nutrient deficiency.

Below-Ground Symptoms - Below-ground signs of SCN include dwarfed or stunted roots and fewer nodules, which can also result from a number of other causes. Therefore, the only truly unique symptoms of SCN infection are the presence of cysts on the soybean roots. Cysts appear as tiny, lemon-shaped structures that are white initially, then yellow and finally brown as they mature. These cysts are about the size of a pinhead and can be seen with the naked eye, but more clearly using a magnifying glass.

Tiny, white cysts are much smaller than the larger nitrogen nodules in the picture.

SCN Damage/Symptoms

Feeding Damage - SCN damages soybean plants in various ways:

 

  • Extracts valuable nutrients from the plant.
  • Stunts and retards root growth.
  • Disrupts water and nutrient flow through the roots.
  • Suppresses nodulation by nitrogen-fixing bacteria.
  • Creates an entry port for root-rotting organisms.

 

Photo: Soybean field - SCN infestations can result in circular or oval-shaped patterns of yellow, stunted, less vigorous plants.
SCN infestations can result in circular or oval-shaped patterns of yellow, stunted, less vigorous plants.
Photo: Soybean field - SCN infestations can result in circular or oval-shaped patterns of yellow, stunted, less vigorous plants.
Tiny, white cysts are much smaller than the larger nitrogen nodules in the picture.

Related Content

Nematode - Field Sampling


 
 
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