Currently, SCN has been established in only a few fields in the Red River Valley. Measures to slow the spread of SCN into uninfested fields can still be effective. The first step is detection of SCN in order to identify fields where SCN is present. Detection should be followed by actions to limit the spread of SCN and the buildup of populations of SCN where it does occur.

Symptoms and Detection

An essential element for managing SCN is detecting the pest where infestation has taken place. Symptoms of SCN infestation include leaf yellowing and poor plant growth (Fig. 1) and can easily be confused with symptoms caused by soil nutrient deficiencies, iron chlorosis, and seedling and root rot pathogens.

Fig. 1. Foliar symptoms of SCN infestation include leaf yellowing and poor plant growth. The symptoms are very similar to those associated with iron chlorosis (Photo courtesy, Senyu Chen).

Observation of adult females and cysts on the roots of soybean plants and in soil samples are the only accurate way to diagnose SCN infestation in the field. When SCN populations are high, SCN cysts can be found on the roots of soybean plants that are carefully dug, lifted from the soil, and washed to remove soil without disturbing or stripping soil – and SCN cysts from plant roots (Fig. 2).

Fig. 2. Cysts of SCN on soybean plant roots. The cysts are easily stripped from plant roots. (Photo courtesty Greg Tylka, ISU and Plant Health Intiative).

A hand lens is helpful for confirming that cysts are present. Additional sampling for management purposes requires that soil be collected and SCN egg counts determined in the laboratory. Procedures for soil sampling for SCN are very similar to those for proper sampling for soil nutrient levels. Detailed instructions for sampling can be found at:
http://www.planthealth.info/scn_scout_pooryields.htm

Soil samples to be analyzed for the presence of SCN should be sent directly to:

Nematology Laboratory  
Southern Research and Outreach Center
35838 120th St. 
Waseca, MN   56093

SCN Management

Avoid spreading SCN from infested to noninfested fields. If only one field or a limited area in a farm is infested, planting perennial crops such as alfalfa in the infested field may slow spread of SCN. If possible, plant noninfested fields first and power wash equipment after working infested fields. Cleaning tillage and harvest equipment can slow dispersal of SCN in soil carried on the equipment. Although it probably has limited usefulness in the Red River Valley, reduced tillage or no-tillage management can minimize movement of soil to limit the spread of SCN within and between fields. Although it is probably impossible to prevent the eventual spread of SCN throughout the region, slowing the spread can be important in reducing losses to this pest.

Crop rotation and the use of resistant varieties are currently the most effective tools for managing SCN once a field is infested. However, the alternate year corn-soybean rotation commonly planted in southern Minnesota is not adequate for reducing SCN numbers unless resistant soybean varieties are planted. Corn, small grains, sunflower, canola, and sugar beet are all non-hosts for SCN, will not support SCN reproduction, and are also useful as rotation crops. Research undertaken by Dr. Senyu Chen at the Southern Research and Outreach Center indicates that crop sequences including multiple years of these crops can substantially reduce SCN numbers. Currently the number of SCN resistant soybean cultivars available in maturity groups adapted to the Red River Valley is limited. However, if resistant soybean cultivars are available, they should be included in crop rotations planted in SCN infested fields. The University of Minnesota soybean breeding program and commercial breeders are working to make additional cultivars available in early maturity groups.

SCN, Sudden Death Syndrome, and Brown Stem Rot

The interaction of SCN with a number of other soybean diseases including Fusarium root rots, brown stem rot (BSR) and sudden death syndrome (SDS) will complicate management of these diseases. The role of SCN in infection by root rotting fungi of soybean is recognized but poorly understood. It is thought that wounding and feeding by SCN increases susceptibility to Fusarium root rots. There is a widespread but poorly understood relationship between the presence of SCN and the occurrence of SDS. Various explanations have been given for the relationship including increased susceptibility to SDS caused by SCN feeding, spread of the SDS pathogen by SCN, and a symbiotic relationship between the SDS pathogen and SCN. SDS has been found with increasing frequency in southern Minnesota and is second only to SCN as a yield limiting disease of soybean in Illinois, Indiana, and Iowa. Recently, researchers in Iowa have found that infestation by SCN increases the severity of BSR, a disease that is widespread throughout Minnesota. Infection by SCN appears to reduce the effectiveness of varietal resistance to BSR and increase the severity of BSR in susceptible varieties.

The introduction of SCN presents a serious challenge to soybean productivity but it is a challenge that can be dealt with.
           
Additional information about the soybean cyst nematode can be found on the web at: http://www.planthealth.info/scn_basics.htm. Useful publications that cover SCN identification, sampling, and management can be found University of Minnesota Soybean website at http://www.soybeans.umn.edu and on the Soybean Plant Health Initiative Website at:
http://planthealth.info/scnguide/

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