In past years, sudden death syndrome (SDS) has appeared during the last week of July or the first week of August in Iowa. Therefore we anticipate symptoms of SDS will begin appearing in the state within the next couple of weeks. Although we do not expect SDS to be as widespread or as severe as the 2010 growing season, there have been some Iowa counties that have received higher-than-normal precipitation. We expect the risk of SDS in these counties to be higher since disease development is favored by wet conditions.
The first symptoms of the disease are usually found on more compacted and low areas of the field. First symptoms are seen on the leaves of infected plants as scattered, yellow spots between leaf veins. Large sections of leaf tissue between veins turn yellow as spots grow together. These yellow blotches soon turn brown, but the veins remain green. Eventually the leaves die and drop, but the petioles remain on the stem. Infected plants are also easily pulled from the soil because the roots are rotted. When split lengthwise with a knife, the internal tissue of the main or tap root will be gray to reddish brown, not healthy white.
There are no in-season management options for SDS, but scouting is still important for several reasons.
Plant pathologists and agronomists continue research to improve our understanding of the biology of the fungus that causes SDS and develop improved management options for the disease. The Iowa State University (ISU) soybean breeding program continues to develop and release germplasm with improved resistance to SDS that is available to all private soybean breeding companies. These Iowa State scientists collaborate with scientists at other universities. Most of the SDS research at Iowa State is funded by soybean checkoff dollars from state, regional and national organizations, namely the Iowa Soybean Association, the North Central Soybean Research Program and the United Soybean Board.
Key research advances from the last five years of research on SDS at Iowa State include: