The first bellwether trial in the multidistrict litigation targeting Monsanto Co. with claims that its herbicide Roundup causes cancer got underway with some fireworks Monday, as the federal judge overseeing the case threatened the lead plaintiffs lawyer in the case during her opening statements with sanctions.

U.S. District Judge Vince Chhabria of the Northern District of California interrupted plaintiffs lawyer Aimee Wagstaff of Andrus Wagstaff multiple times, including calling a pair of sidebar conferences, in attempts to keep her opening presentation focused on the subject of the first phase of the trial: Whether or not plaintiff Edwin Hardeman's lawyers can prove that his use of Monsanto's Roundup herbicide caused his non-Hodgkins lymphoma. Chhabria bifurcated the trial to frontload the causation question while leaving questions of Monsanto's potential liability and damages for a potential later phase in the trial.

Monday morning, the judge accused Wagstaff of attempting to shoehorn in evidence—such as any efforts Monsanto has made to shape regulations concerning Roundup—that he'd ordered excluded from the trial's first phase. At a break a little more than an hour into Wagstaff's presentation with the jury out of the courtroom, Chhabria threatened to cut short Wagstaff's opening remarks.

“You have crossed the line so many times in your opening statements it's obvious that it's deliberate,” Chhabria said. ”If you bring in material in your opening statement that is inadmissible in phase one, your opening statement will be over,” he said.

The judge returned from the brief break after entering a show cause order on the docket in the case, asking Wagstaff to respond in writing as to why she should not be sanctioned “for willfully and repeatedly violating the limitations on the subject matter that could be discussed in her opening statement.” Wagstaff must respond in writing to the show cause order by 8 p.m. Monday. She completed her opening statements without incident.

The stakes are high for Monsanto's parent company Bayer AG. The company was hit last year with a $289 million verdict in San Francisco Superior Court in a Roundup case outside the MDL proceedings. However, the state court judge overseeing the case later slashed that amount by more than $200 million.

Chhabria, for his part, has shown skepticism concerning the plaintiffs' scientific evidence pretrial. In July, he narrowly allowed plaintiffs' cases in the MDL to move forward, but called evidence that glyphosate—the active ingredient in Roundup—causes non-Hodgkin's lymphoma “shaky” but “admissible.” He wrote that plaintiffs had a “daunting challenge” to prove causation.

In Hardeman's case, the plaintiffs also have complications they did not have in the case that yielded the blockbuster verdict. Dewayne “Lee” Johnson, the plaintiff in the state case, was diagnosed with non-Hodgkin's lymphoma, or NHL, after spraying a Monsanto herbicide similar to Roundup in his job as a school groundskeeper. Johnson's case was fast-tracked for trial because of his dire health prognosis. Hardeman, by contrast, is in remission from cancer and developed NHL after using Roundup on his own property to clear poison oak from hiking trails and his driveway.

Brian Stekloff, a lawyer at Wilkinson Walsh + Eskovitz who is representing Monsanto in the Hardeman trial, said during his opening that the plaintiff had significant risk factors for NHL, including pre-existing diagnoses of Hepatitis B and C, obesity and old age. He also pointed to data from the Agricultural Health Study, a long-term study of agricultural workers, which found that levels of NHL among those exposed to glyphosate were similar to those in the general population. He also said that NHL cases had remained steady at about 70,000 per year even as the use of Roundup has grown exponentially since the 1990s.

He said, “If the plaintiff's theory was true then the evidence would show you that the rates of non-Hodgkins lymphoma are increasing.”