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SDS attacking soybean crop




Indiana Correspondent


WEST LAFAYETTE, Ind. — Anyone running a Google search for SDS will come up with a dozen definitions for the acronym, but the one hitting soybean growers hardest is sudden death syndrome.

A disease first observed in Arkansas in 1971, it moved into the Midwest in 1982, causing an estimated 25 percent yield reduction. It has been found in Illinois, Indiana, Iowa, Kansas, Kentucky, Mississippi, Missouri, Ohio and Tennessee. Yield losses of up to 80 percent have been reported from affected areas of those fields.

Although soybean breeders are working to develop SDS-resistant cultivars, progress has been slow. Loren J. Giesler, extension plant pathologist at the University of Nebraska-Lincoln, said SDS is a fungus that overwinters in residue and soil, and is translocated to foliage.

SDS symptoms appear between bloom and pod fills, usually between the R3 and R6 growth stages. It can affect individual plants, small groups of plants or plants in circular to oblong patches in a field. Small, yellowish interveinal blotches in the leaves are the first signs usually recognized. Eventually yellow areas between the veins become brown as the tissue dies.

Root rot will appear on the tap root, followed by discoloration of the vascular tissue contained in the outer stem area and extend up from the soil line. Pods may be aborted and plants may defoliate early. More prevalent during cool, wet growing seasons, SDS is favored in high-yield environments.

Iowa State University field agronomist Mark Johnson predicts that yield-wise, Iowa’s soybean crop won’t break any records this year. Many bean fields in his 10-county area were not planted until June and remain short; other fields planted earlier and in better conditions are showing signs of SDS.

Complicating SDS identification is the fact brown stem rot, stem canker, charcoal rot and chemical burn can produce foliar symptoms. Brown stem rot differs from SDS symptoms by darkened pith and less discoloration; stem canker is associated with spore mat within the stem that are visible, according to the American Phytopathological Society (APS).

Disease management


APS reports management options for SDS are limited. Some practices, such as fungicides applied in furrow during planting and treatments, may reduce the risk of SDS damage but they will not prevent the disease. Early planting in cool, wet soils makes soybean plants vulnerable to infection. Fields with no history of SDS should be planted first; if SDS has been a problem, those fields should be planted last.

Compacted soils impede water percolation and restrict root growth. A heavy rain when the soybean has reached the reproductive stages will saturate compacted areas, promoting SDS development.