• Wisconsin counties in which SCN has been detected.

  SCN appear as white or yellow “pearls” on roots. Click on image to view a larger version.

  Slow row closure is a common symptom of SCN

  Soybean cyst nematode is the #1 pest of soybean in the USA
• Causes yield loss each year
• Symptoms not obvious in many cases
• 10 to 20% yield loss without obvious symptoms
• Symptoms blamed on other potential problems
• Unexplained yield decline most common symptom
• Diagnosis: soil analysis and inspection of roots
• SCN-resistant soybean varieties are available

Diagnosis

• Soil samples can be taken at anytime.
• Plants must be dug, not pulled, to properly inspect roots for SCN.
• Results are reported as number of eggs per 250 cc (cup) of soil.
• The white stage of the SCN can be observed on soybean roots at or shortly after flowering.
• The number of SCN on roots will increase until late pod stage and then decline.
• SCN will change color progressing from white to a yellow color.

SCN Population and Management Actions

The benefit of SCN resistant varieties is related to SCN population in a field, soil type and genetic form of SCN.

Crop rotation can slow the increase of SCN on susceptible soybean varieties, but seldom is effective to reduce SCN after high populations have become established.

High potassium fertility can minimize yield loss at low SCN levels, but not if populations reach high levels.

It is important to know the level of SCN infestation in a field and adjust crop rotation, crops grown, and soybean varieties planted to match the level of infestation.

Table 1. Risk assessment of soybean cyst nematode by soil population and soil type

Note: yield loss of resistant varieties will be modified by the virulence of SCN population in a specific field

SCN-resistant varieties
Several sources of resistance used by soybean industry

• PI 88788 (95% of varieties)
• Peking
• Cyst-X

Current SCN resistance = suppression of SCN reproduction.

• Races of SCN; forms of SCN found that can reproduce on soybean varieties with the PI88788 source of resistance.
• Races affect performance of specific SCN resistant varieties.
• Rotate SCN resistant varieties with different sources of resistance.
• Rotate varieties with PI88788 resistance if varieties with other source of resistance are not available.

SCN Distribution

Soybean cyst nematodes are not distributed uniformly in fields. It is possible to have a problematic field, but miss detection because samples were collected in the wrong spot.

The areas shaded white are intended to provide examples of where SCN can be concentrated in highest numbers within a field. These are areas that should be sampled to increase the likely-hood of detection in soil samples.

• Field entryway: SCN introduced with soil on equipment
• Low spots and flooded areas: Soil is washed into low spots and SCN becomes concentrated.
• Fence lines: SCN can be carried with windblown soil.
• SCN populations are higher if soil pH approaches 7.0 and decline as soil pH approaches 6.0 and below.