A recent report from an international health organization has bolstered the argument that a commonly used herbicide should be dropped from use on Marin public lands, say opponents of relying on chemicals to control non-native vegetation.

The debate about whether the county and the county’s largest water district should use the herbicide glyphosate to control plants that easily overrun native vegetation in parks and open space has lasted for decades.

Proponents of using the herbicide (which routinely is called a pesticide) say that it’s the most effective way to control non-native plants, from a cost-benefit basis as well as a practical basis. Land managers in the Marin County Open Space District say that it’s nearly impossible to eradicate non-natives such as broom varieties using mechanical means and hand pulling. The proponents say that applying glyphosate judiciously creates little risk to the environment.

Opponents of using glyphosate say that’s just not true. They point to studies that show a causal relationship between glyphosate and health hazards. Proponents, however, point to studies that show the opposite—that glyphosate is safe.

The issue has bubbled for decades, periodically coming to a boil. The temperature of the debate increased recently when the county planned to apply glyphosate judiciously to control vegetation in the Ring Mountain Preserve between Corte Madera and Tiburon.

The debate over whether to use glyphosate had focused on the Marin Municipal watershed. Protecting the county’s main watershed and reducing fire danger from non-native plants on Mount Tam is one thing, say opponents of chemical control, but using glyphosate in the Ring Mountain Preserve is unacceptable and endangers visitors.

Anti-pesticide proponents are circulating a petition calling on the Board of Supervisors to come out against using the pesticide. At a recent board meeting, Supervisor Katie Rice, who represents the preserve area, said that the county should review its integrated pest management plan. The county is already committed to a reduction of pesticides in parks, but the Open Space District has no such similar mandate, although land managers in the county view using glyphosate as a last resort.

The Marin Municipal Water District (MMWD) has been reviewing its non-native control policies, and the district board is expected to take up the issue soon.

What makes this time different from all other times is a report from the cancer research group of the World Health Organization. In March, the International Agency for Research on Cancer (IARC) said that its most recent investigation of glyphosate data shows that the chemical is a “probable carcinogen.” That’s an increase in the hazard level from the organization’s previous classification of glyphosate as a “possible carcinogen.” That increase adds immediacy to the call to stop using the chemical in Marin.

Almost as soon as the report went public, critics from the chemical industry blasted the research, saying that IARC cherry-picked data contained in previous studies. The controversy continues, but opponents of using glyphosate in Marin say the IARC report should be viewed as just one more nail in the glyphosate coffin.