A first of its kind trial over whether Monsanto herbicide Roundup caused a groundskeeper's lethal cancer is scheduled to begin July 9 with opening remarks by attorneys.

The stakes are high for Monsanto, which could face massive losses should it have to pay out damages over the product, whose main ingredient is glyphosate, a substance which some say is dangerously carcinogenic.

Dewayne Johnson, a 46-year-old father of two, says he is sick because of contact with Roundup, which he used for two years from 2012 as a groundskeeper for the Benicia school district near San Francisco, his lawyer Timothy Litzenburg told AFP.

Thousands of lawsuits targeting Monsanto are currently proceeding through the US court system, according to American media.

Whether the substance causes cancer has been the source of endless debate among government regulators, health experts and lawyers.

Californian law allows for an expedited procedure when a party is facing imminent death, and Johnson's is the first targeting Roundup to use that law and reach trial.

A jury of five women and seven men was empaneled Thursday, and presentation of evidence will commence after opening remarks, according to the San Francisco court.