Proceedings of the Vertebrate Pest Conference

The anticoagulants diphacinone and chlorophacinone (0.01% and 0.005% concentrations) are used extensively for control of California ground squirrels (Spermophilus beecheyi). Because of concerns of risks to nontarget wildlife, there is a need to develop baiting strategies that minimize the amount of bait applied, while still providing a high level of control. In 1997 and 1998, we conducted laboratory studies to determine the effect of timing and number of bait applications, and amount of bait given per application on the efficacy of 0.01% diphacinone for California ground squirrels. Results suggest that only two applications with 4 or 5 d between applications are necessary to achieve control. This is in contrast to the label recommendation of three to four applications with 48 h between applications (spot baiting), and two applications with 2 or 3 d between them (mechanical broadcast baiting). Furthermore, in our study, squirrels only required a small amount (less than 4 g of bait) per application to receive a lethal dose. Field studies are underway to test this baiting strategy and various bait application methods in the field.