A retired Manitoba farmer is hoping to lead a class action lawsuit against the company that owns Monsanto, alleging he developed cancer after using Roundup on his yard and field to get rid of weeds.

The proposed class action was filed in Manitoba's Court of Queen's Bench by Merchant Law Group on Aug. 26 against Bayer, the German multinational company that now owns Monsanto, which created the herbicide Roundup.

The suit says the Lorette-area farmer used Roundup on a weekly basis on his family farm as directed, being "particularly careful while mixing and spraying" it and using protective gear.

He was first diagnosed with non-Hodgkin's lymphoma in 1996 and underwent chemotherapy and radiation treatments until 2006.

Now 71, he retired in May after his cancer came back and he once again underwent chemotherapy.

Court documents allege Bayer and Monsanto have failed to warn about potential risks and endangered the plaintiff and other class members by continuing to claim that "Roundup creates no unreasonable risks to human health."

The key ingredient glyphosate — a broad-spectrum herbicide — has been classified by the World Health Organization as "probably carcinogenic to humans."

The defendants "knew or ought to have known that Roundup products were unsafe when used in the manner specified," the suit claims.

It also alleges that "the Roundup manufactured and supplied by the defendants was defective in manufacturing" and that was "a proximate cause of the plaintiff's injuries," including the development of his cancer.

Research says glyphosate non-carcinogenic: Bayer

In an emailed statement on Wednesday, Bayer Canada said it is aware of the statement of claim filed in Manitoba.

"While we have great sympathy for the plaintiffs, glyphosate-based herbicides are not the cause of their illnesses and we will vigorously defend our products," the company's statement said.

"Glyphosate has been extensively studied globally by scientists and regulators, and results from this research confirm it is not carcinogenic. We firmly stand behind the safety of glyphosate-based products and as a company devoted to life sciences, assure Canadians that their health and the environment are our top priority."

The Manitoba lawsuit says there are hundreds of litigations underway in the United States against the defendants. Bayer faces Roundup cancer lawsuits by more than 13,400 plaintiffs across the United States, according to a July Thomson Reuters report.

In May of this year, a jury ordered Monsanto to pay $2 billion US to a couple who blamed Roundup for their cancer. A judge later reduced that award to $86.7 million US.

And last year, a northern California court ruled in favour of a groundskeeper's claim that Monsanto's weed killer caused his non-Hodgkin's lymphoma. He was originally awarded $289 million, an amount later reduced to $78 million.

Health Canada is required to reassess herbicides every 15 years. In 2017, it approved the continued use of glyphosate in Canada. At the time, the department received eight notices of objection, which prompted a scientific review.

In January, Health Canada scientists again rejected arguments that the ingredient in herbicides like Monsanto's Roundup causes cancer if the substances are used as directed.

Roundup and glyphosate products are registered for use in 130 countries.

The proposed class action has yet to be certified by a Manitoba court.

It is seeking damages for personal injury, costs, and economic loss.