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Sudden death syndrome developing in Minnesota soybeans

Agriculture.com Staff 08/09/2006 @ 10:55am

Sudden death syndrome (SDS) was confirmed in two southern Minnesota soybean fields on Aug. 3 and 4.

One field is in Steele County south of Owatonna and the other is in Brown County south of New Ulm. Both sites are in relatively low parts of fields with potentially poor drainage. Sudden death syndrome was reported in the same Steele County field in 2004.

These are the only two locations where SDS has been noted this year to date, but this disease is likely developing at other locations too. Survey work by Dr. Jim Kurle from the University of Minnesota and Minnesota Department of Agriculture Pest Report survey team previous years suggests SDS occurs most frequently in the south-central part of Minnesota, but the distribution of this disease in the state is uncertain. Sudden death syndrome was first confirmed in Minnesota in 2002.

Symptoms of SDS are found on leaves and roots of soybean. The foliar symptoms of SDS are most obvious. Chlorotic (yellow), diffuse spots develop between the veins on leaves, and the leaves may become cupped or curled. The spots typically enlarge and become brown lesions surrounded by yellow areas. Leaves often detach from the petioles as the disease progresses. The foliar symptoms can appear very similar to symptoms of brown stem rot (BSR), but the pith remains white in plants infected with SDS while the pith becomes brown, especially at the nodes, in plants infected with BSR.

In addition, in plants infected with SDS, brown-gray discoloration develops just under the surface and into the vascular tissues of the lower stem. Root rot symptoms of SDS are not as obvious, but are important in the development of this disease. SDS may cause root rots, and in some cases a blue fungal growth can develop on infected roots in moist soils.

Sudden death syndrome symptoms have been reported to develop in Minnesota in early- to late-August. It is difficult to predict when, where and how severe SDS will become due to the many environmental and other factors that influence disease development.

Some factors that often seem to favor development of SDS in the Midwest include:

  • Compacted soil and poor drainage
  • Moderate to high populations of soybean cyst nematode
  • Wet soil conditions after planting
  • Environments favorable for high soybean yields
  • Soybean cultivars with poor ratings for SDS resistance
  • Early planting
  • Heavy rainfalls occasionally throughout summer

SDS is caused by a soilborne fungal pathogen that infects through the roots. The infection can move up the roots and into the stem. The pathogen causes root rot, and reports from Illinois suggest that yield loss can result from root rot alone in the absence of severe foliar symptoms. In addition, the SDS pathogen also produces a toxin which is translocated up the plant and is a primary cause of the foliar symptoms and leaf drop. Yield losses from SDS can be significant. Kurle previously compared soybean yields in parts of fields with and without symptoms of SDS, and his preliminary work suggests that yield losses can be greater than 60%.

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