Soybean sudden death syndrome (SDS) - Fusarium virguliforme
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Soybean sudden death syndrome (SDS) can cause significant yield losses. In 2009, a Michigan grower noted a greater than 50 percent yield loss; with areas symptomatic for SDS yielding on average 27 bu/acre compared to non-symptomatic areas which produced 60 bu/acre. In this CAT Alert article, we will discuss how to identify SDS, factors that influence disease development and management strategies.
Signs and symptoms of soybean sudden death syndrome
SDS symptoms consist of initial pale green to chlorotic (yellow) spots that progress to interveinal chlorosis and necrosis (Figure 1). Leaves may also demonstrate cupping similar to some viral symptoms (Figure 1). Symptoms typically develop during late reproductive stages but under certain environmental conditions, symptoms may develop earlier. As the disease progresses, leaflets detach from the petioles. Roots will have root rot symptoms, however, this cannot be used to distinguish it from other root rot pathogens. Late in the season SDS affected plants may show signs of infection by the production of gray to blue Fusarium virguliforme spore masses on the tap roots (Figure 2). Brown stem rot (BSR) can produce similar foliar symptoms but can be distinguished from SDS by observing split stems. In SDS affected plants, the internal root and vascular tissue of the lower stem will often appear gray to brown while the pith remains white. In plants affected by brown stem rot (BSR), pith tissue will turn a dark brown color. It is possible for plants to be infected with both SDS and BSR and a number of other pathogens can cause similar disease symptoms, so it is best to have samples tested at a diagnostic clinic.
Within the United States, SDS is caused by the soilborne fungus Fusarium virguliforme. Several other closely related Fusarium species have also been reported to cause SDS in South America, however, they have not been detected in the United States. Fusarium virguliforme is capable of overwintering on plant debris in the soil and as chlamydospores (a type of tough spore). The fungus infects plants early in the season and can kill seedlings affecting plant stands. As plants begin to grow, root rot symptoms will develop. In addition to root rot symptoms, the fungus produces a toxin that is translocated up into the foliage which produces the foliar symptoms. It is possible for plants to be infected without the production of foliar symptoms. The fungus does not move up beyond the soil line and is not seed transmitted. SDS development is favored by cool and moist conditions. Although SDS disease severity may be increased in the presence of soybean cyst nematode (SCN), SDS can and does develop in the absence of SCN.
Distribution of SDS in Michigan
Fusarium virguliforme has been confirmed in soybeans in southern Michigan counties, Berrien, Cass, St. Joseph, Van Buren, Allegan and Monroe (Figure 3). It is expected that Fusarium virguliforme is present in other Michigan counties particularly in the south. In order to characterize the extent of SDS in Michigan and to determine the diversity and aggressiveness of the fungus, please send samples or provide locations for sampling (see details at the end of this article). Isolates collected from Michigan will ultimately assist in the development of resistant varieties and improved management options.
SDS management considerations
Correct identification of the disease is essential in formulating an appropriate management strategy. Have a sample tested by a diagnostic clinic. The best control option is to prevent or minimize the chance of introducing Fusarium virguliforme onto your property. Prevent soil movement from areas with known or unknown infestations by pressure washing equipment between farms and if possible between fields. Use clean seed with no soil clods, although Fusarium virguliforme is not seed transmitted, soil from infested locations may contaminate seed. If you have identified the presence of SDS, select resistant or partially resistant cultivars. If possible, reduce excessive soil moisture with drainage and by carefully monitoring irrigation applications. Minimize soil compaction, which has been demonstrated to be associated with SDS development. Plant fields with a history of SDS last; reducing exposure to cool, wet conditions early in the season may reduce severity of SDS. Research is continuing on the use of fungicide and nematicide seed treatments. If you have SCN, manage fields to reduce numbers through the use of SCN resistant varieties and crop rotation. Crop rotation does not seem to reduce SDS inoculum pressure. Keep records of problem areas in a field, sketch a map of the area affected. Only by record keeping will you know if your management strategy is working.
Free diagnostics for suspect SDS samples
Suspect SDS-affected plants can be submitted for free diagnosis as part of a Project GREEEN funded project. Follow the submission guidelines on the MSU Diagnostic Services website. Please include entire plants in you shipment. To prevent soil from touching the foliage, roots can be placed into a separate plastic bag and secured at the soil line with a rubber band.