Environmental groups say state regulators ignored science and broke public health laws when they approved a controversial pesticide for strawberry fields.

Lawyers for a coalition of pesticide reform and farmworker groups argued Thursday that officials favored the input of the chemical's manufacturer, Arysta LifeScience, over scientists' recommendations.

The groups are asking an Alameda County Superior Court judge to vacate approval for the use of methyl iodide, which kills bugs, weeds and plant diseases and is used by some growers of tomatoes, peppers and other crops. The state Department of Pesticide Regulation approved its use before Gov. Arnold Schwarzenegger's term ended.

Environmentalists say regulators violated state law by mischaracterizing methyl iodide's approval as an emergency action in order to gain approval before a new administration takes office.

The state said it conducted large amounts of research before approving the chemical in 2010, despite opposition from its own scientific advisors and an independent scientist panel who said it can cause cancer.

Judge Frank Roesch expressed skepticism about the research process, saying it appeared that regulators didn't properly explore alternatives.

"Did you consider not approving methyl iodide? I don't see it," Roesch asked. "Absent that, I don't see how you can prevail in the lawsuit."

The judge gave the state until Jan. 20 to show it was not required to consider alternatives under the California Environmental Quality Act.

Methyl iodide was approved for use by the U.S. Environmental Protection Agency in 2007 as a replacement for the fumigant methyl bromide, which is being phased out by international treaty because it depletes the ozone layer. Environmental groups have asked the EPA to reconsider the approval of methyl iodide.

Methyl iodide is registered in 47 other states.

California's $1.6 billion strawberry industry would provide one of the biggest markets for the chemical. The fumigant has been applied five times in the state since it was approved, including twice in Fresno County.