“Why the Fuss?” Explained

First-generation anticoagulant rodenticides (FGARs) were developed in the 1940s and are considered “multiple dose” rodenticides, because they typically require multiple feedings by a rodent over time to obtain a lethal dose. Second-generation anticoagulant rodenticides (SGARs) were developed in response to resistance issues reported with the FGARs, primarily warfarin.  CA Department of Pesticide Regulation registered bromadiolone in 1982, brodifacoum in 1983, difethialone in 1997, and difenacoum in 2008. In general, SGARs are more acutely toxic than FGARs because they are designed to be lethal after a single feeding instead of after multiple doses. Since it takes several days for a rodent to die after feeding on an SGAR, rodents may feed on the SGAR bait multiple times before dying. As a result, rodent carcasses may contain residues of SGARs many times over the lethal dose. If a non-target predator feeds on a rodent carcass containing a lethal concentration of an SGAR, the non-target predator can also be impacted by the rodenticide.