University of Missouri scientists have linked glyphosate, the active ingredient in Roundup herbicide, to increases in fungi on the roots of soybean plants and in soil around those roots.

"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," says Pat Donald, Missouri plant pathologist.

Fusarium fungi are almost always found in soybean fields, but elevated levels can cause diseases in susceptible plants, and can lead to lost yields due to sudden death syndrome and other root rots, says Donald.

Yields weren't affected in these studies. But "potential yield impacts in subsequent seasons due to high soil fusarium populations, resulting from continued use of glyphosate, need further investigation," according to Donald.

Soil scientist Robert Kremer says the study revealed that fungi levels build over the growing season.

"We need to look at it more and see whether there's a buildup of the organism from year to year," Kremer says.