Maine Just Restricted Four Rat Poisons Over What They Were Doing to Owls

On June 5, 2026, Maine's Board of Pesticides Control voted to restrict consumer use of four specific rodenticide active ingredients: brodifacoum, bromadiolone, difenacoum, and difethialone. The restriction took effect June 16, 2026, under a law (LD 356) that directed the Board to address rodenticide use statewide. Products containing these four chemicals can now be sold only by licensed Restricted-Use Pesticide dealers, and bought or used only by Maine-licensed private and commercial applicators — general consumers and ordinary retail dealers are out of that chain entirely. The decision wasn't about whether these products kill rodents effectively; it was about what else they were killing along the way.

What makes this class of chemical different

All anticoagulant rodenticides work by blocking an enzyme the body needs to recycle vitamin K, which is essential for blood clotting; without it, exposed animals eventually die of uncontrolled internal bleeding. Second-generation anticoagulant rodenticides (SGARs) — the class that includes all four chemicals Maine just restricted — are considerably more potent than older first-generation versions, engineered specifically so that a single feeding can deliver a lethal dose instead of requiring repeated exposure over several days. That potency is effective pest control, but it comes with a side effect: SGARs accumulate and persist in the liver of whatever eats them, staying biologically active well after the original animal has died.

The rat isn't the only thing eating the poison

That persistence is exactly what turns a rodenticide into a wildlife problem beyond the rodent it's aimed at. A poisoned rat or mouse doesn't necessarily die instantly, and a slowed-down, dying rodent is an easy target for a predator — meaning the poison effectively gets passed up the food chain in a process researchers call secondary or relay toxicosis. A 2022 Cornell University study found that 68% of red-tailed hawks tested in New York carried detectable anticoagulant rodenticide residues, describing the exposure as widespread among the state's raptors. A separate 2022 study of powerful owls found dead around Melbourne, Australia detected anticoagulant rodenticides in 83.3% of the birds tested, with brodifacoum — the same compound now restricted in Maine — the most common compound found, often at toxic or potentially lethal levels. Notably, the researchers pointed out that powerful owls rarely eat rodents at all; they concluded the poison most likely reached the owls through poisoned possums instead, meaning the exposure pathway extends well beyond the target species the bait was ever meant for.

What actually changes for someone buying rat poison in Maine

The practical effect for Maine residents is straightforward: the four restricted SGARs simply aren't available over the counter anymore. A homeowner can no longer pick up a box containing brodifacoum, bromadiolone, difenacoum, or difethialone at a general retailer: that product line is now reserved for state-licensed applicators, which in practice usually means going through a licensed pest control professional rather than a DIY purchase. Older first-generation anticoagulants and non-anticoagulant rodenticide options generally remain available for consumer purchase, so the restriction targets this specific, most-potent chemical subclass rather than rodenticides as a category.

Part of a broader 2026 pattern, not an isolated decision

Maine's move follows a similar direction taken elsewhere this year. In March 2026, Australia's national pesticide regulator concluded that SGARs pose an unacceptable risk to non-target wildlife, including native owl species, and recommended restricting their classification. In the UK, rules that took effect January 1, 2026 require buyers of professional-use rodenticides to hold recognized proof of competence before they can purchase them. None of these actions ban rodent control outright — they're each narrowing who can buy the most potent, longest-persisting chemical tier, while leaving other rodent-control tools in place.

• As of June 16, 2026, Maine restricts consumer sale and use of four second-generation anticoagulant rodenticides (brodifacoum, bromadiolone, difenacoum, difethialone) to licensed applicators only.
• SGARs block vitamin K recycling, causing fatal internal bleeding, and are potent enough to kill with a single feeding — but they also persist in a poisoned animal's liver well after death.
• A 2022 Cornell study found 68% of tested New York red-tailed hawks carried anticoagulant rodenticide residues; a 2022 Australian study found residues in 83.3% of Melbourne-area powerful owls tested.
• Secondary (relay) poisoning doesn't require a predator to eat the targeted rodent directly — the Australian owl study traced likely exposure through poisoned possums instead.
• Maine's restriction is part of a wider 2026 pattern, alongside new SGAR risk findings in Australia and stricter purchase requirements in the UK.

Whatever the regulatory tier, a licensed professional is generally better positioned to choose and place rodenticide safely than an unassisted DIY approach. A free Sevacorp inspection is a reasonable starting point for figuring out what a given rodent problem actually calls for.

• Sources:
• Maine Department of Agriculture, Conservation and Forestry — "Important Update: New Restrictions on Certain Rodenticides and Herbicides" — https://content.govdelivery.com/accounts/MEDACF/bulletins/41d7da3
• Maine Audubon — "Breaking News: Maine Audubon Celebrates Rodenticide Restrictions" — https://maineaudubon.org/news/breaking-news-maine-audubon-celebrates-rodenticide-restrictions/
• Cornell University (Cornell Chronicle) — "Rodenticide poisoning widespread among NY's red-tailed hawks" — https://news.cornell.edu/stories/2022/07/rodenticide-poisoning-widespread-among-nys-red-tailed-hawks
• PubMed (Cooke et al., Science of the Total Environment) — "Anticoagulant rodenticide exposure in powerful owls" — https://pubmed.ncbi.nlm.nih.gov/35026248/
• University of Florida IFAS Extension (Polk County), Naturally Florida podcast — "Rat Poisons and Wildlife: What's the Big Deal?" — https://sfyl.ifas.ufl.edu/polk/natural-resources-and-conservation/naturally-florida-podcast/s2/s2-e7---rat-poisons-transcript/