Ingredient in Roundup weed killer going on California list as cancerous

FRESNO, Calif. (KFSN) -- Starting July 7, Glyphosate, the active ingredient in Monsanto's popular Roundup weed killer, will be added to California's list of chemicals known to cause cancer. Products that contain the compound will have to carry a warning label by next year.

The agriculture company has vowed to continue its legal fight against the designation required under Proposition 65.

The move will not keep the chemical off fields or garden store shelves. That's because the state law does not set rules on how chemicals are used, it just requires a warning label.

Monsanto calls the decision "unwarranted on the basis of science and the law."

Scott Partridge, Monsanto's vice president of global strategy, said in a statement that glyphosate does not cause cancer and there's no need to list it as harmful in California.

"This is not the final step in the process," Partridge said. "We will continue to aggressively challenge this improper decision."

Attorney Michael Baum, who represents more than 300 people who claim a loved one became sick or died from exposure to Roundup, also the fight to protect Californians is not over.

He said that the state's failure to set the proper risk level would undermine protections California put in place by listing harmful chemicals.

Glyphosate has no color or smell. Monsanto introduced it in 1974 as an effective way of killing weeds while leaving crops and plants intact.

It's sold in more than 160 countries, and farmers use it on 250 types of crops in California, the nation's leading farming state.

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The Associated Press contributed to this report.