Monsanto, which is in the process of being acquired by Bayer, also faces litigation in the United States from farmers, members of their families and others who claim that Roundup is connected to non-Hodgkin’s lymphoma. The litigation has led to embarrassing questions about whether the company had engaged in ghostwriting of news articles and academic papers.
The rise of Roundup has reshaped agriculture. Two decades ago, Monsanto introduced its line of Roundup Ready seeds, which were genetically engineered to be resistant to glyphosate. That meant that farmers could spray Roundup after crops emerged from the ground, killing weeds later in the growing season. Its use soared around the globe in key crops like corn, cotton and soybeans, from the United States to Brazil to Australia.
Glyphosate has become so ubiquitous that weeds are becoming more resistant to it, leading Monsanto and other companies to develop alternatives. That process, too, has been challenging. New versions of an old herbicide, dicamba, developed by Monsanto and BASF as an alternative to glyphosate, have divided farmers and led to litigation that it is damaging some crops.
It is no surprise that Monsanto, which has been the most outspoken corporate proponent of using genetically modified crops to make it easier to spray pesticides, has few fans among environmentalists. And even though Europe has almost entirely shunned genetically modified crops, glyphosate is still the most popular weed killer on the Continent.
“Our planet is being poisoned by Monsanto,” said Teri McCall, a California avocado farmer whose husband, Jack, used Roundup for years and died in 2015 after suffering from non-Hodgkin’s lymphoma. Ms. McCall, a plaintiff in the lawsuit against Monsanto, was in Brussels to meet with European lawmakers, accompanied by her lawyers from Baum Hedlund, a Los Angeles firm.
“At the very least it needs to have a warning label so people can make an informed decision,” she said. “My husband was under the impression that it was safe.”
Monsanto vigorously rebuts the cancer claims and has lamented the popular opposition in Europe, which is at odds with the opinions of regulators. Two agencies, the European Food Safety Authority and the European Chemicals Agency, have signed off on the safety of glyphosate. And the European Commission, the executive branch of the European Union, has recommended reauthorizing glyphosate, though the decision falls to the member states.
“The conclusions of E.F.S.A. and ECHA that glyphosate should not be classified as carcinogenic is in line with the conclusions of many other regulatory bodies, both inside and outside the E.U.,” said Anca Paduraru, a spokeswoman for the European Commission. “We would welcome a country that intends to vote against to explain the scientific reasons.”
Little in the world of pesticides comes without bitter dispute, with companies and their critics both attacking the positions of public agencies.
The cancer claims against Roundup spring from an assessment by the International Agency for Research on Cancer, a branch of the World Health Organization, which categorized glyphosate as a probable carcinogen in 2015. Monsanto and its allies have assailed the finding as an outlier.
Likewise, environmental activists have attacked European regulators, saying they rely too heavily on the word of industry giants when making safety decisions. The European Food Safety Authority was harshly criticized after The Guardian reported that its assessment had partly been copied from Monsanto.
“They quoted long bits and pieces,” said Sven Giegold, a German member of the European Parliament from the Green Party. “You would be committing fraud if you did this for your Ph.D.”
The food safety agency has said that consulting with companies whose products are being considered is the normal course of doing business, and that nothing in its review was out of the ordinary. Bernhard Url, the executive director of the agency, has called the criticism “the latest in a series of efforts to discredit the scientific process behind the E.U. assessment of glyphosate.”
Monsanto and its competitors, many of which also sell glyphosate products after Monsanto’s patent expired years ago, now see the process as divorced from rational discourse.
“We have observed with increasing alarm the politicization of the E.U. procedure on the renewal of glyphosate — a procedure which should be strictly scientific but which in many respects has been hijacked by populism,” Monsanto wrote in a recent letter to the European Parliament.
When the reauthorization vote comes, Germany could be pivotal. The country’s position has been complicated by its recent national election; Chancellor Angela Merkel is still trying to put together a government, one that is expected to include the Green Party, which takes a dim view of glyphosate.
Joachim Rukwied, president of the German Farmers’ Association, said Ms. Merkel had assured farmers at a meeting this year that she supported glyphosate.
“She is for prolongation of glyphosate for the next 10 years,” he said. “I hope this will be the position of Germany.”
The Green Party has its own ideas, but neither politicians nor executives were inclined to predict the outcome.
“The use of pesticides is a big concern,” Mr. Giegold said, adding that he opposed prolonging glyphosate’s approval in Europe. “I think France and Italy, if they sustain their position, it will depend very much on Germany.”
Because of an editing error, an earlier version of a picture caption with this article described incorrectly the men shown with Teri McCall. One of the men is a fellow plaintiff, not a lawyer.