For related articles and more information, please visit OCA’s Genetic Engineering page and our Millions Against Monsanto page.

The heavy use of Monsanto’s Roundup herbicide appears to be causing harmful changes in soil and potentially hindering yields of the genetically modified crops that farmers are cultivating, a government scientist said on Friday.

Repeated use of the chemical glyphosate, the key ingredient in Roundup herbicide, impacts the root structure of plants, and 15 years of research indicates that the chemical could be causing fungal root disease, said Bob Kremer, a microbiologist with the U.S. Department of Agriculture’s Agricultural Research Service.

Roundup is the world’s best-selling herbicide and its use has increased as Monsanto, the world’s biggest seed company, continues to roll out herbicide-tolerant “Roundup Ready” crops.

Roundup Ready corn, soybeans and other crops are beloved by farmers because farmers can spray the herbicide directly onto their crops to kill surrounding weeds, and Roundup Ready corn and soybeans varieties make up the vast majority of those crops grown in the United States.

But as farmers have increased their use of Roundup Ready crops and Roundup herbicide, problems have started to rise. One of the biggest problems currently is spreading weed resistance to Roundup. But Kremer said the less visible problems below the soil should also be noted and researched more extensively.

Though Kremer said research to date has not shown that glyphosate directly causes fungal diseases that limit crop health and production, but the data suggests that could be the case.

“We’re suggesting that that potential certainly exists,” Kremer said in a presentation to the annual conference of the Organization for Competitive Markets, held Friday in Kansas City.