Plant Disease: Soybean Cyst Nematode

Taxonomy:

Distribution:

Marks on map indicate SCN present

Life Cycle:

• There are three main stages to the life cycle of the soybean cyst nematode.


• The cycle starts in the spring when temperature and moisture levels are adequate for egg hatch.


• Once a juvenile penetrates a soybean root, it moves through the root to the vascular tissue.


• In the vascular tissue the nematode establishes a feeding site.


• It then continues to feed and swell and eventually the females burst through the root tissue.


• The egg-filled body of the dead female is what is referred to as the cyst.


• Each cyst can contain up to 400 eggs.

Symptoms:

Field with SCN symptoms

• The first indication of a problem is when yields are low.


• Low levels of SCN may not produce visible aboveground symptoms, yet yields may be reduced.


• High SCN levels can cause plant stunting and yellowing.


• Aboveground symptoms can be confused with damage from compaction, nutrient deficiencies, drought stress, low-lying wet areas, herbicide injury, and other plant diseases.


• Circular to oval areas of stunted, yellowed plants can be observed.


• Areas of SCN injury often are elongated in the direction of tillage practices, since the cysts are spread by tillage equipment.

• Symptoms include stunted roots with fewer nitrogen-fixing nodules on the roots.


• SCN infestation may increase susceptibility to soil-borne fungal infections.


• The only unique symptom or "sign" is the presence of the adult females and cysts on the roots.

• Adult females appear as lemon-shaped bodies on the roots and are initially cream-colored.


• They later turn yellow and finally tan to brown as they mature to form the cyst.


• These are seen with the unaided eye and are much smaller than nitrogen nodules.

• Observation of adult females and cysts on the roots is one way to confirm SCN infestations in a field.


• In most SCN-infested fields in Nebraska, females are evident on roots by July 4 or after, however, the absence of cysts on the roots does not mean a field is free of SCN.


• In fields with a low population, very few cysts may be found on the roots and they may be easy to miss by visual observation.


• The only way to know a field is free of SCN is with a thorough soil test.

Management:

• There are many management practices to help reduce nematode infestation.


• Please refer to Neb Guide G99-1983-A.