SCN

Effects of SCN in Soybeans
Courtesy of:
www.gov.on.ca/OMAFRA/english/crops/facts/90-119f3.gif

Last updated by
Nick Dolezal
on January 30, 2002

Common Names of Soybean Cyst Nematodes:
-Nematodes
-SCN

Causal Agent:
Species:
Heterodera glycines

Phylum:
Nematoda

Order:
Tylenchida

Host Range:

Here are some of the alternate crops, ornamentals, and weeds that SCN can survive on:

Field Crops	Ornamentals	Weeds
Soybeans	Sweet Pea	Vetch
Common Vetch	Sage	Pursiane
Peas	Caraway	Mullein
Edible Beans	Black Locust	Henbit
Sweet/Yellow Clover	Cup-Flower	Corn Cockle
Lupines	Foxgrove	Pokeweed
Cowpeas	Chinese Latemplant	Pigweed
Clover	Poppy	Toad flax
Birdsfoot-trefoil	Delphinum	Chickweeds

Geographical Range:

SCN originated in Asia and is now found throughout the world. SCN can be found in Japan, Colombia, United States, Taiwan, Egypt, and many other regions similar in climate to the areas listed. The nematode's ability to survive and spread throughout the world can be attributed to it's movement with soil and the wide number of host they can survive on.

Symptoms:

As seen on the photo on the top of this page, Soybean Cyst Nematodes can be devastating to a soybean crop. Often times, if a soybean field looks even in growth, and healthy, SCN symptoms may not be evident until the the crop is harvested and yield less than anticipated are discovered. In most situations, SCN can be diagnosed by observing chlorotic yellowing on soybeans in certain, often low-lying, areas of the field. Upon closer observation, the chlorosis can be seen as interveinal yellowing on the leaves. Often times the farmer or crop scout may place the blame for this condition on compaction, alkaline soil or iron chlorosis, herbicide injury, or even excessive moisture stress. during the right time within the pathogen's life cycle, the cysts will be visible to the naked eye. They can be found as little white spots on the roots. These spots are not to be mistaken for larger, nitrogen fixing nodules, which are more obvious when compared to SCN cysts.

Dissemination:

Basically, anything that can move soil, can transport and relocate nematodes. Wind, water, field equipment, humans, migratory birds, and other animals are just a few of the vehicles for nematodes to be moved on. Generally, whole cysts are not transported. The microscopic nematodes moving with the items listed above are what infects a soil and eventually soybeans

Disease Cycle:

The cyst part the SCN life cycle is really the dead body cavity of what is left of the once microscopic, female roundworm. the cyst serves as a protective covering for the young eggs which are harbored inside. Once the eggs hatch, the juveniles will search for roots to bury their stylet into. Each cyst may contain up to 500 eggs. The search for a root to feed on must not take long otherwise the small roundworm will die due to starvation. Once a root is found and the nematode begins to feed, it will molt into adulthood. Here the nematode will either develop into a male or female. Females remain immobile, embedded into the root. Males will pull away from the root and search for a mate to fertilize. Once this occurs, the cycle starts over again. This whole process can take from 24-30 days.

Control Measures:

SCN can never be totally taken out of a field once introduced. In order to control SCN, many measures can be taken. Jim Smolik, a nematologist at South Dakota State University, says that the best control of the parasitic roundworm is a good basic cultural practice, rotation. Rotation from non host crops like wheat or corn can break up the life cycle and constant reproduction of SCN. Soybeans resistant to SCN are available and should be used in a field with a history of SCN however, a good rotation schedule should be followed along with the most resistant varieties. The elimination of other host plants will reduce the number of nematodes produced. Also, the cleaning of equipment between transport from field to field will greatly reduce the spread of SCN. Anything that will reduce soil movement from field to field will help in limiting the nematode's movement. Below is an ad from the Soybean Cyst Nematode Coalition urging farmers to take the SCN test to see if they need to implement a control for the pest or not.

http://nematode.unl.edu/scnextension.htm Recent Research-Summary: