California's Department of Pesticide Regulation (DPR) announced on 15 September that it has completed a set of risk-mitigation actions on tribufos, an organophosphate registered solely as a cotton defoliant. The product stays on the market, but its label is tighter: allowable application rates are reduced, and irrigation and weeding are prohibited immediately after application, both changes aimed at cutting farmworker exposure.

Tribufos, sold under the trade names DEF and Folex, was first registered by the US Environmental Protection Agency in 1985 and re-registered in 2006. It remains under federal registration review and is approved in 17 cotton-growing states, including California, Texas, Arizona, Georgia, Mississippi and Louisiana. Health advocacy groups have flagged cancer and neurodevelopmental concerns for farmworkers, handlers and nearby residents, part of the sustained scrutiny organophosphates have faced at federal and state level for more than a decade.

The state's move follows a 2023 round of federal label amendments. DPR's own assessment concluded that unmitigated exposure risks remained under the federal label, and California, which may impose stricter rules than Washington, proposed the additional restrictions finalised this month. DPR describes the action as closing a long-running legacy risk-assessment item, to be logged in a forthcoming Continuous Evaluation and Mitigation Update, rather than a cancellation.

It lands in a more assertive year for DPR's post-registration review. In August 2026 the agency confirmed that every holder of a paraquat-dichloride registration in California, including Syngenta, had voluntarily cancelled, after a re-evaluation opened in November 2024 flagged possible links between paraquat exposure and thyroid effects and birth defects, and risks to birds and other wildlife. The last cancellation took effect on 6 August 2026, starting a two-year sell-through of existing stock. Paraquat is banned outright in more than 70 countries, including the EU since 2007.

Neither tribufos nor paraquat is a large-volume molecule globally, but together they show DPR working through a backlog of legacy organophosphate and bipyridylium pesticides under pressure from farmworker and environmental advocates. The department is also taking public nominations for future reviews through a new Pesticide Science Committee that met for the first time in August 2026.

Photo: Lance Cheung, USDA / Wikimedia Commons (Public domain)

Source: Global Agriculture