Every company that sold paraquat in California has canceled its state registration, marking the beginning of a phase-out of one of the state's most heavily used herbicides, the California Department of Pesticide Regulation announced. The final registrant withdrew its product on August 6, and the department confirmed the full set of cancellations four days later.
California is the largest user of paraquat in the country, according to the Center for Biological Diversity, and its use is concentrated. More than three-quarters of the state total is applied in eight San Joaquin Valley counties, farm regions around Fresno, Bakersfield, and Visalia, where a large share of residents live in or near agricultural communities. Those households and the licensed applicators who handle the product are the first to be reached by this decision.
The change does not empty shelves overnight. Under state law, licensed dealers may keep selling canceled products for up to two years after each cancellation takes effect, and growers using remaining stock must follow all label directions and existing state and federal rules. In practical terms, exposure risk winds down over a period rather than stopping on a single date.
The Regulatory Path That Led Here
The state opened a formal reevaluation of paraquat in November 2024, then released two preliminary scientific assessments the following month. Those preliminary reports identified a potential association between paraquat exposure and thyroid effects and birth defects, and flagged risks to other organisms, with the most significant concern for birds.
Reevaluation gives the department authority to demand new studies from manufacturers. It set a June 5 deadline for registrants to submit data addressing gaps in its human health toxicology database. Rather than produce that data, companies began withdrawing their products. Syngenta, the longtime maker of the brand-name product Gramoxone, canceled its California registration effective April 1 and has said it will stop making and selling paraquat herbicides. Generic products from other suppliers followed.
"We need the right data to identify where there are risks," department Director Karen Morrison said in the announcement. California Secretary for Environmental Protection Yana Garcia said the state will keep moving "toward pest management practices that protect health and our ecosystems."
Nathan Donley, environmental health science director at the Center for Biological Diversity, said in a statement that California and other states "are taking aggressive steps to protect people," while criticizing the pace of federal action. Paraquat remains registered nationally, and the Environmental Protection Agency has not banned it.
What the Parkinson's Evidence Does and Does Not Show
This is where precision matters. The state's rationale for cancellation rests on data gaps, thyroid effects, birth defects, and harm to wildlife. Parkinson's disease is the concern that has driven public attention and litigation, but it is not what the department cited as the trigger.
The research base is genuinely mixed. Multiple case-control studies have reported an association. One population-based study of 829 Parkinson's patients and 824 community controls in three Central California counties used state pesticide-use records to estimate residential and workplace proximity to paraquat spraying and found an association with the disease. Laboratory work shows paraquat can cross the blood-brain barrier and damage the dopamine-producing neurons lost in Parkinson's. Results have not been uniform, though. Analyses within the federal Agricultural Health Study, a long-running cohort of farmers and their spouses, found no significant association, and the manufacturer disputes any causal link.
An association is not proof of cause. What can be said accurately is that a substantial body of epidemiological and mechanistic evidence points in one direction, that the evidence is contested, and that no study establishes that any individual person's Parkinson's disease was caused by paraquat.
The distinction is not academic for readers seeing advertisements from law firms recruiting plaintiffs. Thousands of lawsuits are pending nationwide, and no court verdict has settled a scientific question. Anyone weighing that decision should treat it as a legal matter with a lawyer and a medical matter with a neurologist, and should not assume the two answers will line up.
Paraquat's acute toxicity is not in dispute. There is no antidote, and swallowing a small amount can be fatal. That risk is why it is a restricted material that only licensed dealers may sell and only licensed applicators may use.
Who Carries the Exposure Burden
Farmworkers and licensed applicators face the highest exposure, followed by people living near treated fields, where spray drift is the main route. Many of these households in the San Joaquin Valley are Latino, lower-income, and less likely to have a nearby neurologist or occupational medicine specialist.
A spill in March in the Siskiyou County town of Dorris made the acute risk concrete. A 120-gallon drum fell from a truck; roughly 60 gallons reached a roadway, and passing vehicles spread the herbicide through the downtown area. Officials ordered a shelter-in-place for about 600 residents, including those in schools, and closed a highway for the day. Some people reported respiratory symptoms and sought care, and no serious injuries were reported.
Growers face a different kind of burden. Paraquat is valued precisely because it kills weeds resistant to other herbicides, and it is used across California orchards, vineyards, and field crops. Replacing it will mean higher costs for some operations and more mechanical or integrated weed control for others, which is why the state has tied the phase-out to research funding rather than simply removing the product.
Residents who worked with paraquat or lived beside treated fields should tell their clinician about that history, especially if they notice tremor at rest, slowed movement, stiffness, changes in handwriting, or a reduced sense of smell. Those symptoms have many causes and do not indicate Parkinson's on their own, but an exposure history is useful information for a doctor. People without insurance can start with a county health department or a federally qualified health center, which charges on a sliding scale. Anyone who swallows or is doused with a pesticide should call 1-800-222-1222 or 911 immediately.
The department is funding research into alternatives through a grants program whose current application window closes September 1, and it continues to assess other pesticides through its continuous evaluation process. Under a state law requiring a faster review, the full paraquat reevaluation must be completed on or before January 1, 2029.
Key Questions Answered
Is paraquat banned in California now? Not exactly. Every manufacturer canceled its registration, so no new product can be sold in the state. Licensed dealers may sell remaining stock for up to two years after each cancellation, and growers may use it under existing rules.
Why did the companies withdraw? The state required them to submit new scientific data by a June deadline to close gaps in its human health toxicology database. They canceled their registrations instead of providing it.
Did California find that paraquat causes Parkinson's disease? No. The state's preliminary assessments cited potential associations with thyroid effects and birth defects, as well as risks to birds and other wildlife. The Parkinson's evidence is an association reported in several studies and not found in others.
Who is most at risk from exposure? Licensed applicators and farmworkers who handle it directly, and residents near treated fields exposed through spray drift. Use is concentrated in eight San Joaquin Valley counties.
What symptoms should exposed workers watch for? Acute poisoning is a medical emergency. For long-term concerns, resting tremor, slowed movement, muscle stiffness, smaller handwriting or reduced sense of smell are worth discussing with a clinician alongside the exposure history.
Does this affect food safety for shoppers? Paraquat is applied before harvest as a desiccant and weedkiller, and federal residue limits are set. The health concerns driving state action center on applicators and nearby residents, not grocery shoppers.
What happens next? California's full paraquat reevaluation must be completed on or before January 1, 2029. The Environmental Protection Agency has not banned paraquat nationally, and Vermont enacted the first state ban.
