Sudden death syndrome (SDS) was confirmed in two southern Minnesota soybean fields on August 3 and 4, 2006.  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.   SDS 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 the Minnesota Pest Report survey team from the Minnesota Department of Agriculture in previous years suggests that SDS occurs most frequently in the south central part of Minnesota¹, but the distribution of this disease in Minnesota is uncertain.  SDS 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. 

SDS 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: (i) compacted soil and poor drainage, (ii) moderate to high populations of soybean cyst nematode, (iii) wet soil conditions after planting, (iv) environments favorable for high soybean yields, (v) soybean cultivars with poor ratings for SDS resistance, (vi) early planting, (vii) heavy rainfalls occasionally throughout summer.

Early to moderate stage symptoms of sudden death syndrome (SDS) on Minnesota-grown soybean (Photo: Dean Malvick)

Chlorotic and necrotic symptoms of SDS on soybean leaves and brown discoloration on inner stem tissues from soybean grown in Steele County Minnesota (Photo: Dean Malvick)

SDS is caused by the soilborne, fungal pathogen Fusarium solani f.sp. glycines.  This fungal pathogen infects through the roots, and the infection can move up the roots and into the stem.  Thus, this 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.  Dr. Jim 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%.

SDS is a challenge to manage.   Yield losses from SDS can be reduced by planting cultivars with relatively high levels of tolerance or partial resistance to SDS.  Crop rotation has not shown consistent benefits for SDS management.  In addition, it may be beneficial to plant later than normal where SDS has been a problem, improve soil drainage and reduce compaction if possible, and to plant SCN-resistant cultivars. 

¹http://www.mda.state.mn.us/pestsurvey/pestreports/default.htm

printer-friendly PDF version