The short guide to sudden death syndrome in soybeans
Posted October 3, 2014
Posted October 3, 2014
First discovered in Arkansas in 1971, sudden death syndrome (SDS) now affects nearly every state where soybeans are grown. SDS is an important disease because it can overwinter in soil, creating larger infected areas with each growing season until most of the field is diseased. SDS is most severe when soybeans are planted early into cool, wet soils and when heavy mid-summer rains saturate the soil.
SDS is caused by the soilborne fungus Fusarium virguliforme. SDS overwinters in crop residue and freely in the soil. When the warm weather hits in the spring, fungi germinates and infects nearby soybean roots.
Symptoms almost never appear before flowering. Heavy rains during reproductive stages are conducive to SDS development. The fungus in the wet soil produces toxins that translocate to leaves and produce foliar symptoms. The fungus itself does not climb the stem more than a few centimeters above the soil line.
Symptoms first appear with the yellowing and defoliation of upper leaves. These first symptoms are often confined to a few sporadic areas throughout the field – often in wetter or more compacted zones.
As the disease progresses, other symptoms include:
There are three strong indicators that a plant is infected with SDS:
There are soybean varieties with low field tolerance all the way to full resistance.
Planting early predisposes the soybean to infection. Always plant the fields last where SDS has been found in previous years.
Correcting soil compaction and water permeability problems may reduce the risk for SDS (Abney, Shaner, Westphal, and Xing 3).
Fungicides applied to foliage have no effect and fungicides applied in furrow during planting or as seed treatments have limited effects.
Rotation does not appear to significantly reduce SDS.
The extent of yield loss depends on the severity and timing of the disease relative to plant development. Early season development of SDS means the flowers and young pods might abort. Later season SDS development means fewer seeds per pod or smaller seeds. The earlier the prevelance of SDS, the more yield will be reduced. (Abney, Shaner, Westphal, and Xing 1).
Note: When a field has both SDS and soybean cyst nematode present, SDS is much more severe.
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