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Sponsored: SCN and SDS: The Connection

The presence of soybean cyst nematode (SCN) in a field substantially increases your risk of developing sudden death syndrome (SDS) and reducing your soybean yield potential.

Soybean cyst nematode infestations are generally observed in lighter soil classes where a soybean crop has been grown continuously without being rotated to nonhost crops. Fields with large areas of SDS are often the result of an SCN infestation.

The presence of SCN can be difficult to diagnose before damage occurs. Positive identification of SCN requires submitting a soil sample for nematode analysis. However, the additional confounding issue of a race structure within the nematode population adds a level to the diagnostic situation since some soybean varieties are resistant to specific SCN races. Race identification is also a costly endeavor.

Incidences of SDS increase under stressful growing conditions of susceptible host crops.

Recommended management practices include rotating from soybeans to a nonhost crop such as alfalfa, corn, oats, sorghum, sugarbeet or wheat. The rotational alternatives will differ based on geography.

Other SCN management tactics include planting an SCN-resistant soybean variety and minimizing crop stress by maintaining adequate soil fertility, properly managing water and field drainage, and controlling disease and pest pressure.

According to the University of Minnesota Extension’s Soybean Cyst Nematode Management Guide, it may take as many as five years to reduce SCN populations to pre-infestation densities.

While there are few management options, and presently no cure for SDS, correctly diagnosing the disease in the current season can help manage its spread in future years.

Caused by the soilborne fungus Fusarium virguliforme, SDS likely infects soybean plant roots one week after emergence, but above-ground symptoms rarely appear before midseason (generally after R5). Rains during a crop’s reproductive stage cause the fungus to produce toxins that are then transferred to the leaves, causing symptoms more often referred to as interveinal chlorosis. 

Because early symptoms of the disease can be symptoms of other diseases or can mimic chemical burn, it’s important to examine the inside of the stem and taproot to correctly diagnose SDS.

Dig up the soybean plant exhibiting symptoms and split the stem in half lengthwise. If the stem is a tan to brown color with the central pith remaining white to cream, the plant is infected with SDS. When SDS-infected plants are freshly dug, a blue mold indicating the presence of the SDS fungus may be observed on below-ground plant parts.

In fields with a history of infection, manage planting dates and soil drainage and plant a variety that shows tolerance to SDS. For more information, contact your local Mycogen Seeds commercial agronomist or trusted agronomic adviser.

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