EFFICACY OF ZINC PHOSPHIDE BAITS TO CONTROL VOLES IN ALFALFA - AN ENCLOSURE STUDY

The efficacy of broadcasting zinc phosphide (Zn3P2) grain baits as an acute rodenticide to control gray-tailed voles (Microtus canicaudus) i n alfalfa (Medicago sativa) was assessed. A total of 428 voles was dis tributed within 18, 0.2-ha enclosures having a 2+ year stand of plants . Single, pre-bait (0.0% Zn3P2) and test-/control-(2.0/0.0% Zn3P2) bai t broadcasts (11.2 kg ha(-1)) were applied within enclosures 18 and 20 days following final vole distribution. At 14 days later, a trap-out of the surviving voles was conducted. Only 5.6% of those distributed i n Zn3P2-baited enclosures were recaptured; whereas, 70.1% of those pla ced in control-baited enclosures were retrapped. Analyses of variance for proportions of voles and total voles captured within enclosures yi elded significant main effects for rodenticide. Program CAPTURE estima tes also confirmed significant decreases in vole populations in Zn3P2- baited enclosures. Daily carcass searches yielded 25 and 5 vole carcas ses, respectively, in the Zn3P2 and control enclosures during the bait -exposure period. Three non-target carcasses were found within enclosu res during this period: one Savannah sparrow (Passerculus sandwichensi s) and two vagrant shrews (Sorer vagrans). Results demonstrate the eff icacy and low hazards to non-target passerines of a single Zn3P2 baiti ng to control vole populations in alfalfa.