Insects and Diseases

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Life cycle and biology of SCN

Management of SCN

Soybean Cyst Nematode

Besides reduced yield, often there are no obvious aboveground symptoms of damage caused by SCN. Since there are rarely aboveground symptoms, many infestations go undiscovered for several years. As a result, many producers suffer declining yield for numerous years without knowing that SCN is present in their fields.

Symptoms

Uneven plant height and chlorotic leaves are symptoms caused by SCN damage.

When soybean plants are severely infected, they become stunted, canopy closure does not occur, and leaves may become chlorotic. Unfortunately, SCN is not the only cause of these symptoms. They may also be confused with other crop stresses such as nutrient deficiency, drought, herbicide injury, aphid feeding, and other plant pathogens. Soybean cyst nematode can cause yield reductions of up to 40% on susceptible varieties without showing visible symptoms of nematode damage. The only visible sign of infection is the young female. Young females may not be present on roots at the time of fall soil sampling. White females of SCN are most readily seen in the field starting about 6 weeks after crop emergence. In order to see them, you must carefully dig up the roots with a shovel and remove the soil gently or you will remove the fine roots on which the females are attached to. Although observations of white females will confirm an SCN infestation, it can not tell you much about the level of infestation. Also, if you dig up roots and do not find a white female, that does not mean that SCN is absent. The only way to get a reliable diagnosis is through analysis of a properly-collected soil sample by a professional diagnostic laboratory. Older females, which are brown cysts, are not visible in soil. In high-yielding production fields or during years when soil moisture is plentiful, visible symptoms of SCN damage are rarely seen. Research has shown, however, that yield losses of 15 to 30% on susceptible varieties are common in these fields. Soybean farmers in these situations often notice poor or no longer increasing yields over several years, uneven plant height in the field, a delay in canopy closure, or early senescence (leaf drop). This lack of apparent symptoms is more commonly associated with soybean growth in the Midwest where soils tend to be more fertile and growing conditions less stressful on soybean.

Variety selection is key to managing SCN and SDS in your fields.

Variability of SCN Numbers

Results of analysis of soil samples for SCN population densities will be as variable as any other information you collect relating to a crop. Since the eggs produced by SCN are in clusters of hundreds and the cysts are immobile, it causes the variability to be so high. Variability also occurs since the SCN numbers within that field at that certain time are ever-changing. If two samples are taken from different places in a single field, one may have very high numbers of SCN while the other may have none (figure 1). This is why hot spots develop in heavily infested fields. The presence of a hot spot, however, does not mean that SCN is absent from the apparently “healthy” area. Results from several years of field studies in northern states indicate that high populations of SCN at planting can be expected in area of fields with soil pH levels of 7.0 to 8.0 compared to areas of soil pH 5.9 to 6.5.

Figure 1. High SCN population densities are shown to be consistent with high soil pH.

More Information

How to soil sample for SCN - Link to SCN Management Guide
What is your type? An HG type test for SCN populations (pdf)
Scouting for SCN (pdf)
Two nematode soil sample analysis options (pdf)
Interpreting SCN soil sample results (pdf)
Plant nematode sample submission form (pdf)