SAN FRANCISCO (CN) – On the first day of a federal jury trial over whether Monsanto’s weed killer Roundup caused a California man’s cancer, a San Francisco judge threatened to sanction the man’s lawyer for discussing prohibited evidence in front of the jury.

Calling the attempts to discuss the prohibited evidence “deliberate,” U.S. District Judge Vince Chhabria warned he would cut short attorney Aimee Wagstaff’s opening statement if she continued to disobey orders to limit opening statements to the causes of non-Hodgkin lymphoma, the disease plaintiff Edward Hardeman has.

Minutes later, Chhabria issued a written order directing Wagstaff, of Andrus Wagstaff, to show cause by 8 pm Monday PST why she should not be sanctioned for “willfully and repeatedly violating the limitations on the subject matter” allowed in opening statements.

“Ms. Wagstaff, you have crossed lines so many times in opening statements that it’s obvious it’s deliberate,” Chhabria told her, audibly angry. “EPA – totally inappropriate, totally inconsistent with everything we discussed over the last several months. One final warning. If you cross the line one more time in opening statements with respect to Phase 1, if you bring in material during your opening statement that is inadmissible in Phase 1, your opening statement will be over. I will tell you to sit down, I will tell you your opening statement is over and I will do it in front of the jury. Last chance; final warning.”

In his 2016 complaint, Hardeman, 70, alleges he developed non-Hodgkin lymphoma after spraying Roundup for 26 years around his 56-acre property. The Northern California property sported hiking trails but was infested with poison oak, which Hardeman says required heavy Roundup use. Hardeman, who now lives an hour north of San Francisco in Santa Rosa, was diagnosed with non-Hodgkin lymphoma around Christmas of 2014 after waking up with a golf-ball sized lump on his neck. According to Monsanto, he has been in remission for four years following chemotherapy.

Monsanto counters that Roundup isn’t a risk factor for non-Hodgkin lymphoma. The company, now owned by Bayer, contends most cases of non-Hodgkin lymphoma have no known cause, but points out that Hardeman ticks off four risk factors for the disease: he’s over 60, has a higher than normal body mass index, was exposed to Hepatitis B and, most crucially to Monsanto’s case, had a chronic Hepatitis C infection.

Because Hepatitis C is a risk factor for non-Hodgkin lymphoma, attorneys for both Hardeman and Monsanto discussed Hardeman’s history with Hepatitis C Monday. But Wagstaff’s attempts to go beyond causation, including an attempt to engender juror sympathy for Hardeman and to discredit the U.S. Environmental Protection Agency’s findings that glyphosate is safe – swiftly drew Chhabria’s ire.

Last December, Chhabria granted Monsanto’s motion to split the three trials over which he is presiding into a causation phase addressing only whether Roundup and its active ingredient glyphosate can cause non-Hodgkin lymphoma and whether they caused the plaintiffs’ non-Hodgkin lymphoma, and a second phase addressing Monsanto’s liability and damages.

That means the plaintiffs can’t address some of their key allegations – including that Monsanto has known for decades that Roundup is carcinogenic and that the EPA failed to adequately assess Roundup’s carcinogenicity – until the trial is half over. If the causation evidence isn’t strong enough to warrant a damages phase, the plaintiffs won’t get to address those allegations at all.

Again reprimanding Wagstaff on Monday, Chhabria said he would block her attempt to admit into evidence a photograph of Hardeman’s family displayed to the jury alongside the layout of his Northern California property.

“It was not designed to show the jury the property,” Chhabria said. “It was designed to show the jury his family, and I’m not allowing that to come into evidence in Phase 1.”

During opening statements, both Wagstaff and Monsanto attorney Brian Stekloff, of Wilkinson Walsh Eskovitz, discussed a controversial 2018 study that looked at data from 57,000 glyphosate users culled from the federal Agricultural Health Study [AHS] database.

The 2018 AHS study found no link between glyphosate and non-Hodgkin lymphoma, and due to its size and comprehensiveness, Monsanto contends it is the most “powerful” study in existence on the question of whether glyphosate causes cancer.

But Wagstaff told jurors Monday that plaintiffs’ expert Beate Ritz, an epidemiologist at the University of California, Los Angeles, will testify that the 2018 study is flawed; that it “put quantity over quality” by looking at 50 different chemicals, improperly classified study participants, and used a technique called “imputation” to “guess” at the results of the 37 percent of participants who didn’t respond to follow-up questionnaires.

“She’s going to testify that imputation is not a bad method,” Wagstaff said of Ritz.

“She’s going to tell you that sometimes it’s OK, but she’s going to tell you it’s not OK when you have this many people,” she said. “At some point she will tell you that the test results show that glyphosate protects against cancer.”

Stekloff countered Ritz’s planned testimony during his own opening remarks. Ritz has called the 2018 study “beautiful,” he told the jury, and she acted as an adviser on it “for years.”

“She only started criticizing the Agricultural Health Study after she became an expert in this litigation,” Stekloff said.

In 2015, the World Health Organization’s International Agency for Research on Cancer deemed glyphosate a probable carcinogen, sparking a wave of lawsuits against Monsanto in the United States. Regulators in Europe, Canada and the United States, including the EPA, have concluded glyphosate is safe.

Roundup is the most widely used agrochemical in history. Monsanto introduced it in 1974, and its use exploded after the company introduced “Roundup-ready” seeds in 1996 engineered to resist glyphosate. More than 2.6 billion pounds of glyphosate was spread on U.S. farmlands and yards between 1992 and 2012, according to the U.S. Geological Survey.

The trial continues Tuesday and is expected to last about a month.