Efficacy of Oat and Pellet Anticoagulant Baits Following Treatment with Oat and Pellet Zinc Phosphide Baits: Implications for Secondary Hazard Management

This study was undertaken to demonstrate the efficacy of oat and pellet type anticoagulant baits (0.01% diphacinone) when used following an initial treatment of 2% zinc phosphide oat and pellet type baits for controlling California ground squirrels. Both broadcast oat and pellet anticoagulant treatments following zinc phosphide treatments resulted in apparently good control, although the power of our pellet tests was not strong because of failure in the control plots. Anticoagulant bait use, on a per acre basis, was well below the allowed application rate (10 lbs/acre) because it was applied only where active ground squirrel burrows remained after controlling the entire population with zinc phosphide. No non-target species were found affected by the zinc phosphide or anticoagulant treatments. As a baiting strategy, the combination of zinc phosphide combined with the subsequent selective application of anticoagulant baits was successful. This approach will likely lead to significantly fewer squirrel carcasses with anticoagulant residues, since most are killed with zinc phosphide and subsequently do not pose a significant secondary risk to predators, scavengers, or pets. This baiting strategy has the potential to significantly reduce secondary hazards from ground squirrel baiting