Sudden death syndrome, or SDS, a yield-robbing soybean disease, is showing up in a lot of fields in Iowa this year. It is showing up in field areas that are the low, wetter spots where the disease was initially present and susceptible bean varieties were planted, says Brian Lang, Iowa State University Extension field agronomist at Decorah in northeast Iowa.
This disease starts as an infection through the roots. Soybean cyst nematode can aid this infection process, often making SDS more prevalent in an SCN infested field. "No foliar fungicides will control SDS because the leaves do not have a fungus on them," explains Lang. "The leaf symptoms are due to a toxin produced by the disease present in the root and now, in late August and early September, in the stem region of the plant."
Research shows that a crop rotation with corn does not reduce SDS presence in the field. Selecting resistant soybean varieties is the most important method for future control of SDS. Photos and symptoms are discussed at www.ipm.iastate.edu/ipm/icm/2006/9-18/sds.html. Management of this disease is addressed at www.ipm.iastate.edu/ipm/icm/2003/1-21-2003/sdsmanage.html
How Can You Control White Mold Disease in Soybeans?
As with SDS, white mold disease of soybeans is now showing up in many areas across northeast, east-central and southeast Iowa. Lang says the only foliar fungicide recommended in the past has been Topsin, with the application timed around R1 stage before the white mold symptoms show up.
In reading some foliar fungicide labels, he says Domark carries a label for white mold for an R3 stage application. However, most of the soybeans are now R5 stage or later in growth. Most important at this time is to recognize the problem, take notes, and identify resistant soybean varieties that you can plant in the future. General information and photos on white mold can be found at www.plantpath.wisc.edu/soyhealth/pdf/whitemold_06.pdf. Also a recent article on white mold management was posted by ISU Extension plant pathologist X.B. Yang on the ICM News site at www.extension.iastate.edu/CropNews/2009/0814yangsavi.htm.