A jury in California has awarded $US289 million ($395 million) to a former gardener who said he got terminal cancer from Roundup, a widely used weed killer made by US agro-chemical giant Monsanto.

The jury awarded $US250 million ($342 million) in punitive damages and more than $US39 million ($53 million) in compensatory damages to Dewayne Johnson who was diagnosed with lymphatic cancer at age 42 in 2014, according to news reports.

He is one of hundreds of cancer patients suing Monsanto, with Friday’s development potentially setting a precedent for other cases against the company.

Mr Johnson’s case had been moved up to be heard ahead of others because he is dying.

Mr Johnson blames Roundup for his suffering and accused the company – recently acquired by Germany’s Bayer – of concealing the dangers of the weed killer.

Monsanto vigorously rejects the allegations and says the herbicide glyphosate is safe.

In his job as a gardener he sprayed Roundup and another Monsanto product, Ranger Pro, across a San Francisco Bay Area school district, his attorneys said.

Roundup is the most-used herbicide in the world. Photo: AAP

Last month Judge Vince Chhabria ruled against Monsanto’s request for a dismissal.

The company argued that the more than 400 plaintiffs couldn’t prove that glyphosate, the controversial ingredient in the product Roundup, causes non-Hodgkin lymphoma, a type of cancer affecting white blood cells.

Judge 
Chhabria called the decision “a very close question,” but declined to grant Monsanto’s motion for summary judgement.

He also allowed the opinions of three expert witnesses to be admitted.

In addition to the individual lawsuits there is a class action suit in Chhabria’s courtroom filed by farmers, gardeners and consumers.

-DPA