“We are ready and willing to engage the European Parliament and policy makers in Europe,” said Scott Partridge, Monsanto’s vice president of global strategy, in an email. But, he added, “this particular forum was not set up for substantive discussion related to the regulation and use of glyphosate.”

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.