Glyphosate, the active ingredient in Roundup, was first approved for use in Monsanto's weed killer in 1974. This was the first case tried in court because Johnson was the closest to dying.
Monsanto scientists knew of the cancer risk posed by Roundup as far back as the 1970s, but failed to inform the public and instead engaged in a "deliberate effort to distort the truth" as the weed killer generated hefty returns, Johnson's lawyer, Brent Wisner, told the jury in closing arguments.
Monsanto have insisted that their weedkiller products remain safe for users, with vice president Scott Partridge saying the company would appeal the verdict to "vigorously defend this product".
On Tuesday, the NFF said the U.S. court decision was "in blatant ignorance" of science.
"I think that's something everybody should be scared of, because in this application, however you feel about Monsanto and Roundup, if we apply that same philosophy that courts don't have to use science and evidence to make rulings, then that's a very risky place for society". Among other things, the court allowed Environmental Defense Fund activist Christopher Portier to mislead them by permitting him to serve as an expert witness for the plaintiff Johnson.
The company immediately said it would appeal against the decision and tried to reassure consumers - including those using Roundup elsewhere - that its weedkiller was safe.
Dewayne Johnson has a terminal form of non-Hodgkin lymphoma which he claims he caught after working as a pest control manager at a school. On two separate occasions, he was "soaked" in the weedkiller after a hose broke.
Jurors in state Superior Court agreed the product contributed to Johnson's cancer and the company should have provided a label warning of the potential health hazard. "It's just a matter of time", Wisner told the jury in his opening statement last month. Applying the relatively low standard of proof required in California civil courts that a claim is "more likely to be true than not true", the jury awarded Johnson a $289 million judgment including $250 million in punitive damages against Monsanto, the maker of the herbicide. Johnson declined to take questions from reporters.
Backed by the European Commission, assessments by the European Food Safety Authority and the European Chemicals Agency have not yet found any link between glyphosate and cancer in humans.
Despite the ruling in the U.S., there is still confusion as to whether glyphosate causes cancer and it is still widely used across the UK.
IARC, the World Health Organisation's cancer agency, said in 2015 that glyphosate is "probably carcinogenic to humans," although several worldwide agencies later came to opposing conclusions.