VALLEJO (CBS SF) — Vallejo city leaders were scrambling to find out if and why a potentially toxic weed killer was used on the Mare Island Preserve after a preservationist sounded an alarm, warning people to stay away.

In an impassioned Facebook post, Myrna Hayes, volunteer president of the Mare Island Heritage Trust said the preserve “has been aggressively sprayed with glyphosate,” a chemical herbicide used to kill plants and grasses.

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(Photo Courtesy of Anne von Reiche‎ Mare Island Preserve Community)

Hayes warned people to “steer clear of our Preserve” to avoid exposure to children and pets. She also expressed concern for the chemical’s impact on native plant species, newborn rattlesnakes and the preserve’s honey bee population.

Hayes and a team of volunteers have been taking care of the preserve since its creation in 2008. She told KPIX the spraying of chemicals is evidence of “disconnect between the City of Vallejo and nature.”

Glyphosate is the active ingredient in hundreds of weed-killing products, including Monsanto’s Roundup.

Bayer, the company that owns Monsanto, defends its safety but hundreds cases have been filed against the manufacturer by patients alleging glyphosate-based herbicides are carcinogenic.

Recently, a jury in San Francisco ordered the company to pay $289 million to Dewayne “Lee” Johnson after he filed a lawsuit claiming Monsanto’s herbicides caused his non-Hodgkins lymphoma.

The award was lowered to $80 million and Monsanto has appealed.

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Vallejo mayor Bob Sampayan responded to Hayes’s post, saying he will discuss the matter with city manager Greg Nyhoff in “hopes of finding a solution.”

Meantime, Vallejo councilmember Robert McConnell said he spoke to Hayes and wrote a letter urging the city to stop using the products and, instead, use goats to “remove vegetation on city-owned land to reduce fire damage.”

Hayes’ post has cast a cloud over the preserve’s 11th anniversary celebration on Saturday. Pictures of yellowing grasses where Hayes says the chemicals had been sprayed were posted on the event’s Facebook page.

(Photo Courtesy of Anne von Reiche‎ Mare Island Preserve Community)

(Photo Courtesy of Anne von Reiche‎ Mare Island Preserve Community)

Hayes said she will not be leading visitors on guided tours along the trails Saturday.

“Why should I get people involved in activities on our trails only to expose them to a massive chemical dump,” she said, adding that the visitor center was not impacted.

“Maybe we will pull together an event there,” said Hayes. “It will be a very different kind of celebration, a time of reflection and concern.”

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Meanwhile Saturday, the monthly docent tours of the historic Mare Island Navy Cemetery were still ongoing, as planned.