Edwin Hardeman, the first person to challenge Monsanto’s Roundup in a federal trial, testified Tuesday that he sprayed the herbicide for nearly three decades and got it on his skin before he was diagnosed with cancer.

The 70-year-old Santa Rosa man has alleged that his exposure to Roundup, starting in 1986, when he began applying it to control weeds and poison oak on his properties, caused him to develop non-Hodgkin lymphoma (NHL), a cancer that affects the immune system. In court on Tuesday, Hardeman explained that when he used Roundup, the world’s most popular herbicide, it would at times leak onto him as he sprayed it for several hours a day.

Hardeman’s high-stakes case is considered a “bellwether” trial for hundreds of other plaintiffs in the US with similar claims, which means the jury verdict could affect future litigation and possible settlements. Monsanto, now owned by German pharmaceutical company Bayer, is facing more than 9,000 similar lawsuits across the US.

Hardeman is the second person to successfully bring a Roundup cancer case to trial and the first in US federal court. In an historic verdict last August, a California jury sided with Dewayne Johnson, a former school groundskeeper suffering from a terminal cancer, and ruled that Monsanto failed to warn Johnson of the health hazards from exposure to Roundup, had “acted with malice or oppression”, and was responsible for “negligent failure”. Monsanto was ordered to pay Johnson $289m in damages.

Bayer, which appealed the Johnson ruling, suffered a 30% share drop after the groundbreaking verdict.

In recent years, there has been growing scrutiny across the globe about the potential health impacts of glyphosate, the product sold under the Roundup brand.

Hardeman said he frequently sprayed Roundup on his properties for about 28 years, first for three years at his home in the coastal town of Gualala and then for roughly 25 years in Santa Rosa, where there was a significant amount of poison oak on his 56-acre property.

“It was a regular part of my maintenance,” said Hardeman, who demonstrated for the jury how he used a two-gallon sprayer, spraying above his head and toward the ground. He testified that he would often spray once a month for three to four hours at a time and that he and his wife never hired someone to help with the work: “I enjoyed doing it … I wanted to make sure I was going to get everything up to my own personal standards.”

Sometimes the wind would cause the chemical to “blow back” on his skin, he said, adding that at times it felt as if he was breathing in the chemical.

Hardeman said he stopped using Roundup in 2012. On Christmas Day of 2015, he discovered a swollen lymph node on his neck and the following year was officially diagnosed with NHL, he said.

Unlike Johnson’s trial, which discussed claims that Monsanto worked to suppress damning research and mislead consumers about safety risks, Hardeman’s brief testimony this week did not include any discussions of Monsanto or his beliefs about what caused his cancer.

US district judge Vince Chhabria ruled prior to the start of trial that the plaintiffs were barred from discussing Monsanto’s influence on government regulators and cancer research, restricting the arguments to scientific study and questions about whether Roundup caused Hardeman’s NHL.

During opening remarks last week, Chhabria angrily scolded Hardeman’s attorney, Aimee Wagstaff, accusing her of “deliberately” violating his restrictions on subject matter with “incredibly dumb” comments. The judge threatened to “shut down” the attorney’s speech, said she was “very steely” in her response to his objections, and eventually sanctioned her $500 for “bad faith conduct”.

The judge argued that Wagstaff “crossed the line” with multiple statements, including her discussions of Hardeman’s “personal history”, her reference to internal Monsanto documents, and her explanations of the process behind various regulatory decisions about glyphosate. Chhabria earlier ruled that if jurors decide that Monsanto caused Hardeman’s illness, the jury would learn about the company’s conduct when assessing liability and punitive damages in a second phase.

Hardeman’s lawyers have said these limitations are significantly hurting their case. Wagstaff argued she was acting in good faith during her opening remarks and that there was “ambiguity” surrounding the judge’s orders.

Monsanto has continued to argue that Roundup is safe and in this case has suggested Hardeman’s hepatitis C could be a possible cause of his cancer. Hardeman testified Tuesday that he was cured of his hepatitis in 2006, long before his NHL diagnosis.

One of the plaintiff’s experts, pathologist Dennis Weisenburger, also testified about his research on NHL and cancer on Tuesday, saying: “When you get Roundup on your skin … it will penetrate the cells of the skin, it will get into the tissues, it will then get into the lymph system and into the blood.”

He added: “My opinion is that to the best of medical certainty, I believe that Roundup is a substantial cause of cancer in people who are exposed to it in the workplace or in the environment.”

Hardeman’s team has presented testimony from his doctors, along with a range of experts who have discussed in detail the research linking NHL to glyphosate.

Monsanto is expected to start calling its witnesses later this week.