The Environmental Protection Agency plans to withdraw its approval of a Dow Chemical Co. herbicide, saying it has new information that suggests the weedkiller is more toxic to surrounding plants than previously thought.

In a setback for one of Dow’s newest agricultural products, the EPA this week asked the Ninth U.S. Circuit Court of Appeals to vacate the agency’s approval last year of Dow’s Enlist Duo herbicide, which is designed to be used on genetically engineered crops, so that it may reevaluate the spray.

Dow...