NEW YORK (Reuters) - Bayer AG BAYGn.DE unit Monsanto faces long odds on an appeal blaming an "inflamed" jury and "junk science" for a verdict of $289 million in damages to a man who said the company's Roundup weed killer caused his cancer, according to some legal experts.

FILE PHOTO: Monsanto Co's Roundup is shown for sale in Encinitas, California, U.S., June 26, 2017. REUTERS/Mike Blake/File Photo

Last week’s verdict ended the first trial over whether glyphosate, the main ingredient in Roundup, causes cancer. Monsanto, which says decades of scientific studies have shown Roundup and glyphosate are safe, is facing about 5,000 similar lawsuits nationwide.

Bayer stock fell sharply on Monday following Friday’s verdict in San Francisco Superior Court.

Monsanto said on Monday it planned to challenge the verdict on the grounds that the judge should have barred scientific evidence presented by California school groundskeeper Dewayne Johnson’s lawyers as insufficient.

“Plaintiffs are putting forward junk science that is not based upon the 40 years of safe glyphosate use and studies,” Scott Partridge, Monsanto’s vice president of global strategy, told Reuters. “They attempted to color science with very emotional arguments designed to inflame jurors.”

The company also said statements by Johnson’s lawyers, designed to paint the company in a malevolent light, inappropriately influenced the jurors.

Monsanto could have difficulty getting the verdict thrown out on those grounds, according to some legal experts who said the judge carefully considered whether to allow Johnson’s scientific evidence under California law and reached a defensible conclusion that the jury should hear it.

“This is one of those difficult questions at the margins of science and the judge found the evidence simply wasn’t inadmissible,” said Lars Noah, a law professor at the University of Florida.

Johnson, 46, said in his lawsuit filed in 2016 that frequent use of Roundup caused him to develop lymphatic cancer.

Expert testimony is highly influential in product liability cases, and evidentiary standards exist to prevent juries from making decisions based on theories unsupported by science.

The U.S. Environmental Protection Agency in September 2017 concluded a decades-long assessment of glyphosate risks and found the chemical not likely carcinogenic to humans. However, the cancer unit of the World Health Organization in 2015 classified glyphosate as “probably carcinogenic to humans.”

Monsanto said the plaintiff’s experts should have been excluded because although they mainly cited respected, peer-reviewed studies, they inappropriately cherry-picked results and used unreliable methods to support the position that glysophate causes cancer in humans.

But Alexandra Lahav, a law professor at the University of Connecticut, said it was common for experts to rely on the same studies and reach different conclusions to present to a jury during trial.

Legal experts said a federal judge overseeing other Roundup cases has allowed the same experts to go forward with testimony, even though the standard in federal courts is generally thought to be higher than in state courts.

The evidence rulings might draw the attention of higher courts, both in California and the U.S. Supreme Court, to use the Roundup cases as a way to clarify expert admissibility standards, other legal experts said.

A major question for appellate courts could be whether it is enough for an expert to simply analyze widely accepted peer-reviewed studies to support his own opinion, or whether the expert’s analysis must also be reviewed or otherwise subject to stronger scrutiny, said two California-based defense lawyers, who requested anonymity citing potential conflicts of interest.

Monsanto also took issue with statements by Johnson’s lawyer, Brent Wisner, and some expert witnesses comparing Roundup to tobacco. Wisner told jurors the company would “pop champagne corks” if the verdict was too low.

He also said in court that a Monsanto unit made so-called Agent Orange, a highly toxic herbicide mixture used by the U.S. military 50 years ago in the Vietnam War. The harmful impact included cancers and birth defects.

Wisner on Monday rejected Monsanto’s claims that the jury made its decision on emotional grounds.

“This was a considerate, thoughtful and well-educated jury that looked at the science to conclude glyphosate causes cancer,” Wisner said.

Monsanto’s arguments that remarks by witnesses and lawyers inflamed and prejudiced the jury would likely fall flat, some legal experts said.

David Rosenberg, a professor at Harvard Law School, said editorializing by lawyers in a courtroom needed to be truly egregious for a judge to even consider throwing out a verdict.

“Such remarks are part of the game during trials and I can’t see a single reason why Monsanto would think an appeal would be helpful on those grounds,” Rosenberg said.