Pesticide manufacturers have voluntarily cancelled registrations for products containing paraquat in California — kickstarting a statewide phase-out of the controversial herbicide linked to Parkinson’s disease, according to a California Department of Pesticide Regulation (DPR) announcement on Monday.

Paraquat has been under scrutiny for the last few years due to mounting scientific evidence connecting chronic exposure to the herbicide to Parkinson’s disease and other health problems. It is one of the most widely used herbicides in the US — largely as a tool to kill broadleaf weeds and grasses — and is used in growing soybeans, cotton, and corn as well as in growing grapes, pistachios, peanuts and other crops.

The California DPR began re-evaluating paraquat in 2024 and the department’s preliminary reports found negative impacts to the thyroid system, links to birth defects, and that the herbicide is harmful to wildlife, especially birds. The findings prompted the DPR to require additional studies from pesticide makers on these impacts, and, instead of providing that data, companies began cancelling their registrations beginning in April.