Chemical giant Monsanto has been ordered to pay $2bn (£1.58 billion) to a couple who say they developed cancer after long-term use of a weedkiller.

A jury in Oakland concluded the popular garden staple Roundup Ready caused the non-Hodgkin’s lymphoma that Alva and Albert Pilliod both contracted.

Jurors awarded them each £773,000 in punitive damages in addition to a combined £42m in compensatory damages.

Alberta Pilliod, 76, said after the verdict that she and her husband, Alva, have each been battling cancer for the last nine years and their quality of life has been significantly affected. 

“It changed our lives forever,” she said. “We couldn’t do things we used to be able to do, and we really resent them for that.”

One of the couple’s lawyers, Michael Miller, conceded that the $2bn punitive damages award was likely to be reduced on appeal, but said they are prepared for a long legal battle.

The jury’s verdict is the third such courtroom loss for Monsanto in California since August.

A federal jury in San Francisco ordered the weedkiller maker in March to pay a Sonoma County man £61m.

A San Francisco jury last August awarded £223m to a former golf course greens keeper who blamed his cancer on Monsanto’s Roundup Ready herbicide. A judge later reduced the award by £154m.

The three California trials were the first of an estimated 13,000 plaintiffs with pending lawsuits against Monsanto across the country to go to trial. St Louis-based Monsanto is owned by the German chemical giant Bayer AG.

Bayer said that it would launch an appeal against the verdict.

“The verdict in this trial has no impact on future cases and trials, as each one has its own factual and legal circumstances,” the company said.

The company noted that none of the California verdicts has been considered by an appeals court and that the US Environmental Protection Agency (EPA) considers the weedkiller to be safe.

The EPA reaffirmed its position in April, saying that the active ingredient glyphosate found in the weedkiller posed “no risks of concern” for people exposed to it by any means – on farms, in gardens and along roadsides, or as residue left on food crops.

But a San Francisco law professor said it is likely a trial judge or appellate court will significantly reduce the punitive damages award.

“There is zero chance it will stand,” said David Levine, a professor at the University of California, Hastings School of Law.

He said the ratio between the £1.58bn in punitive damages and £42m in compensatory damages is too high. He said judges rarely allow punitive damages to exceed four times actual damages awarded.