Are Cholecalciferol plus Anticoagulant Rodenticides a Viable Option for Field Rodents?

Abstract

Burrowing rodents, such as pocket gophers (Geomyidae) and voles (Microtus spp.), often cause extensive damage in agricultural, urban/residential, and natural resource areas. Effective management of burrowing rodents typically follows an integrated pest management (IPM) approach that involves a number of tools including rodenticide baiting. However, some of the more commonly used rodenticides have limitations including the development of resistance (e.g., first-generation anticoagulants and strychnine), secondary-toxicity concerns (e.g., anticoagulants), and limited availability (e.g., strychnine). Initial research with combination cholecalciferol plus anticoagulant rodenticides has indicated potential promise at overcoming some of these limitations. As such, we tested the efficacy of several different cholecalciferol plus anticoagulant combinations to determine if they were efficacious in managing Botta's pocket gophers and California voles in both cage and field trials. Two-choice cage trials for California voles indicated that both pelletized (0.03% cholecalciferol plus 0.005% diphacinone, efficacy x = 80%) and bract baits (0.012% cholecalciferol plus 0.002% diphacinone, efficacy x = 70%) containing cholecalciferol plus diphacinone (C+D) were efficacious.Further field testing indicated that C+D-coated bract baits (0.014% cholecalciferol plus 0.003% diphacinone) were highly efficacious for vole control (efficacy x = 85%), while pelletized baits were less promising (efficacy x = 60%). Cage trials indicated that both C+D (0.03% cholecalciferol plus 0.005% diphacinone, efficacy x = 80%) and two concentrations of cholecalciferol plus brodifacoum (C+B1 = 0.015% cholecalciferol plus 0.0025% brodifacoum, efficacy x = 100%; C+B2 = 0.03% cholecalciferol plus 0.0025% brodifacoum, efficacy x = 100%) pelleted baits showed promise as pocket gopher rodenticides. Further field testing of C+D and C+B2 resulted in efficacy significantly >70% (efficacy x = 83% and 75%, respectively), although strychnine (0.5%) applications were the most efficacious (efficacy x = 100%). Collectively, these results suggest that cholecalciferol plus anticoagulant rodenticides are effective options for managing burrowing rodent populations; they deserve further consideration for registration against these potentially damaging species.