Soil Testing and Plant Diagnostic Services


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Soybean cyst nematode egg count recommendations

We recommend that fields be sampled for soybean cyst nematodes (SCN) in the fall before soybeans are planted the following spring.

First scenario

If no SCN eggs are detected or a low egg level is found, soybeans without SCN resistance may be planted if the egg count is below the damage threshold of 500 eggs per cup (250 cm³) of soil.

Precautions

  • If no eggs are detected, sample fields every 2 to 3 years at harvest. This increases the probability of finding the nematode if it is present in the field.
  • Monitor areas of the field where SCN is likely to be introduced, such as field entrances, areas that flood, fencerows or places where waterfowl congregate. If fewer than 500 eggs are detected, sample after a susceptible variety is grown.

Second scenario

If a moderate egg level is found, plant SCN-resistant soybeans if the egg count is above the damage threshold of 500 eggs per cup of soil and below 10,000 eggs per cup of soil. However, if the egg count in the field is greater than 2,000 eggs per cup of soil, reduced yield can be expected even with resistant varieties.

Precautions

  • Rotate sources of SCN resistance whenever possible.
  • If varieties with different sources of resistance to SCN are not available, then grow a different SCN-resistant variety every year soybeans are planted.
  • Resistant varieties increase selection pressure on the nematodes. This can reduce the long-term effectiveness of the resistance.

Third scenario

If a high egg level is found, plant a nonhost if egg counts are above 10,000 eggs per cup of soil. SCN nonhost crops include alfalfa, barley, canola, clover (red, white, ladino), corn, cotton, forage grasses, oats, rye, sorghum, tobacco and wheat. Alternatively, plant only SCN-resistant soybean varieties.

Precautions

  • Rotate nonhost plants with SCN resistant soybean varieties.
  • An HG type "race" test may be appropriate if the egg count is more than 10,000 eggs per cup of soil, and the egg count is increasing despite the use of resistant varieties.

Updated 3/1/11