Grower Evaluation of California Ground Squirrel (Spermophilus beecheyi) Control using Anticoagulant Baits

California ground squirrels continue to present a significant problem for many facets of California agriculture. The use of diphacinone- and chlorophacinone-treated baits remains the most frequent control method for ground squirrels in agricultural settings. Research suggests no difference in efficacy between the two bait types or between broadcast and spot baiting strategies or bait stations. However, these studies were limited in scope and were conducted exclusively on rangeland sites where there is limited availability of alternate food sources. Studies also suggest that a reduced baiting strategy may be as effective as current label recommendations, but this has received only limited attention in field research. We utilized a new approach in conducting field evaluations of anticoagulant baiting efficacy in different agricultural settings and locations throughout the state. We solicited agricultural producers as cooperators to participate in a field-based evaluation to determine if the reduced baiting strategies are effective under specific agricultural operating conditions. Cooperators were trained in a simple research design and monitored to ensure consistent data collection. The training program included a comprehensive manual on squirrel biology, behavior, and control, as well as information on toxicants and legal measures regarding endangered species. An informal survey was sent to cooperators at the end of the project to evaluate their opinions on the efficacy of control methods. We found no difference in efficacy between baiting methods or strategies. Differences in efficacy were found between chlorophacinone and diphacinone and efficacy was lower in nut orchards than in other settings. Despite no difference in efficacy between baiting methods, more cooperators indicated they would use bait stations than other methods in future ground squirrel control operations