September 9, 2010
AMES, Iowa — As soybean sudden death syndrome continues to ravage Iowa fields in one of the worst outbreaks in many years, Iowa soybean growers are increasingly worried about the damage the disease will cause, while others are unsure whether their plants have been infected.
To help answer questions and offer guidance in managing the disease, Iowa State University has produced a video that explains why SDS is so severe this season; tells how to assess and manage SDS; offers practical advice growers can follow now to prepare for next year; and highlights new and ongoing ISU research on the problem.
The video can be viewed on the College of Agriculture and Life Sciences website, or directly at Sudden Death Syndrome video.
In the video, Iowa State plant pathologists Leonor Leandro and Alison Robertson explain how a perfect storm of early planting and wet weather at key points during the growing season created the ideal circumstances for SDS to thrive.
"This year we've had particularly severe SDS due to a combination of early planting into cool, wet soils and the continuation of a wet season with a wet July during reproductive stages that is also thought to favor the disease," Leandro said.
"We also see the disease moving north and west year to year, probably as a result of an increase in the pathogen density in the soils that's building up over the seasons," she said.
Leandro explained that a fungus infects soybean plant roots soon after planting, producing a toxin that later moves up the plant damaging soybean leaves and eventually causing them to die and drop.
Survival of the fungus on corn debris may be another reason why SDS is so widespread this year, she said.
"Recent soybean checkoff-funded research at ISU has shown the fungus can survive on corn kernels and corn stalks. The corn debris is likely allowing the fungus to carry over from year to year, she said.
Growers are unaware plants have the disease until yellow patches start to appear on soybean leaves.
"The yellow patches will extend, turn brown and eventually (the leaf will) die, falling off and leaving a bare stem," Robertson said.
Other SDS symptoms include severe root rot, and sometimes Robertson said the blue color of the fungus may be visible growing on the outside of the root.
If uncertain, she said one way to definitively diagnose SDS is to cut into the soybean plant taproot and observe its color.
"The inside of the root is discolored brown. It's not a creamy white color like you would see with a healthy soybean plant," Robertson said.
Plants that have the disease are likely to experience some yield loss, though Leandro said the extent will depend on how early SDS appeared during the reproductive stages of plant growth.
While SDS can't be treated, Robertson said it can be managed with appropriate variety selection and improved field drainage. In addition, Leandro said Iowa State has developed germplasm with resistance to SDS that has been released for seed companies to develop commercial varieties.
Other resources on SDS can be found at the following links:
Iowa State University Extension Integrated Crop Management News
North Central Soybean Research Program Plant Health Initiative
Iowa Soybean Association — Production Research