Glyphosate Weed Killer Benefits Soil Fungus

Editors / Progressive Farmer 3jan01

A significantly higher incidence of Fusarium has been recorded on the roots of Roundup Ready soybeans during four years of research, according to scientists at the University of Missouri (MU) at Columbia.

"Experiments conducted in 1997 through 2000 at two Missouri locations revealed that Roundup Ready soybeans receiving glyphosate at recommended rates had significantly higher incidence of Fusarium on roots within one week of application compared with" soybeans that did not receive glyphosate, reports Pat Donald, research assistant professor and director of the MU nematology lab.

In the glyphosate-treated fields at research farms near Portageville and Columbia, scientists detected "major colonization by several distinct types of the fungus." Although soil Fusarium populations varied among locations, glyphosate significantly increased numbers at each location", including the Fusarium that causes SDS (sudden death syndrome).

"We're concerned because SDS is showing up everywhere and can be devastating," says Donald, noting that more than 50% of Missouri's soybean acres were planted to Roundup Ready soybeans in 2000. Monsanto has disclosed that the foundation genetics for Roundup Ready soybeans came from a line that is SDS-susceptible. "We're not aware that Monsanto has looked at microbial levels or anything - no non-target organisms - beneath the soil," she says.

"All of the ecological assessment is above ground," says Donald's research partner Robert Kremer, an MU soil scientist and USDA Agricultural Research Service microbiologist. Donald told Rooster.com that they had therefore begun the research to fill this void. And they focused on Fusarium because other researchers have previously reported that glyphosate used on wheat and dry beans has resulted in an increase in this particular fungus. Initially, Donald and Kremer believed the increased Fusarium through glyphosate application could suppress soybean cyst nematode (SCN). "We had observed that some Fusarium in soils can also be associated with lowered levels of cysts," she says. "But it didn't work out that way. In some cases the reproductive rate of SCN dropped as Fusarium numbers rose; in some cases it didn't."

Donald and Kremer emphasize that soybean yields in the experiments were not affected by the application of glyphosate as opposed to conventional herbicide treatments. However, "potential yield impacts in subsequent seasons due to high soil Fusarium populations, resulting from continued use of glyphosate, needs further investigation."