THE world's most widely used weed killer is not responsible for perpetuating sudden death syndrome (SDS) in soybeans, according to recently released research.
A collaborative effort among soybean researchers in the U.S. and Canada found that glyphosate does not increase SDS severity or adversely affect yields in soybean fields. Led by Daren Mueller of Iowa State University, scientists from five midwestern universities and the Ontario Ministry of Agriculture, Food & Rural Affairs participated in the three-year study. Yuba Kandel of Iowa State analyzed the data.
"A common claim out there is that 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 the early reproductive stages.
Fifteen field experiments were conducted in Iowa, Illinois, Indiana, Michigan, Wisconsin and Ontario between 2011 and 2013. Six combinations of non-glyphosate and glyphosate herbicides, including pre- and post-emergence, were tested. Single and multiple applications were also compared.
The data showed that there were no statistically significant effects of herbicide treatments or interactions on SDS severity.
SDS has been on the rise during the last decade. It came to a head in Iowa in 2010, when yield losses in some infected areas reached 40% or more. The disease has cost farmers billions of dollars.
SDS outbreaks have been relatively mild in Iowa over the last three years mostly due to dry summers, the researchers concluded. However, 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."
Selecting seed varieties resistant to SDS offers the best protection, experts said. Breaking up soil compaction zones and extending 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 Assn. senior director of supply and production services. He added that farmers can use the information for weed and disease management.