The world’s most widely used weed killer is not responsible for perpetuating Sudden Death Syndrome (SDS) in soybeans, research shows.

A collaborative effort among soybean researchers in the United States and Canada and found that glyphosate does not increase SDS severity or adversely affect yields in soybean fields. Scientists from five Midwest universities and the Ontario Ministry of Agriculture Food and Rural Affairs, led by Daren Mueller of Iowa State University (ISU) in Ames, participated in the three-year study. Yuba Kandel of ISU analyzed the data.

“A common claim out there is glyphosate is making SDS worse,” said Mueller, a plant pathologist specializing in SDS and other soybean diseases. “This research proves that there are other factors much more important to the development of SDS than herbicide selection.”

The syndrome is caused by a fungus that lives in the soil and enters plants through their roots, causing them to rot. Toxins cause yellow and brown lesions on leaves, and pod fill is compromised. SDS is more prevalent if soil is wet, cold and compacted during germination and early reproductive stages.

Fifteen field experiments were conducted in Iowa, Illinois, Indiana, Michigan, Wisconsin and Ontario, Canada from 2011-13. Six herbicide combinations of non-glyphosate and glyphosate, including pre- and post-emergence, were tested. Single and multiple applications were also compared.

There were no statistically significant effects of herbicide treatments or interactions on SDS severity, data showed.

SDS outbreaks have been relatively low in Iowa the last three years mostly due to dry summers, experts conclude. But that could change this year.

“SDS is largely driven by environmental conditions,” Mueller said. “While the wet, cold spring does play a role in increased risk; to get foliar symptoms, you need moisture during late vegetative/early reproductive stages for higher levels of disease.”

SDS has been on the rise the last decade. It came to a head in Iowa in 2010, when yield losses in some infected areas reached 40 percent or more. The disease has cost farmers billions of dollars.

Selecting seed varieties resistant to SDS offers the best protection, experts say. Breaking up soil compaction zones and extended crop rotations are also effective control methods.

“This unbiased and scientifically-sound study by researchers demonstrates no correlation between glyphosate use and the incidence or severity of soybean sudden death syndrome,” said Dr. Ed Anderson, Iowa Soybean Association senior director of Supply & Production Services. “Iowa farmers who are faced with the challenges of managing SDS can use this information in considering how to manage their weed and disease problems.”