Efficacy of zinc phosphide baits to control voles in alfalfa — an enclosure study

Abstract

The efficacy of broadcasting zinc phosphide (Zn 3P 2) grain baits as an acute rodenticide to control graytailed voles ( Microtus canicaudus) in alfalfa ( Medicago sativa) was assessed. A total of 428 voles was distributed within 18, 0.2-ha enclosures having a 2+ year stand of plants. Single, pre-bait (0.0% Zn 3P 2) and test-/control-( 2.0 0.0 % Zn 3P 2) bait 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 in Zn 3P 2-baited enclosures were recaptured; whereas, 70.1% of those placed in control-baited enclosures were retrapped. Analyses of variance for proportions of voles and total voles captured within enclosures yielded significant main effects for rodenticide. Program CAPTURE estimates also confirmed significant decreases in vole populations in Zn 3P 2-baited enclosures. Daily carcass searches yielded 25 and 5 vole carcasses, respectively, in the Zn 3P 2 and control enclosures during the bait-exposure period. Three non-target carcasses were found within enclosures during this period: one Savannah sparrow ( Passerculus sandwichensis) and two vagrant shrews ( Sorex vagrans). Results demonstrate the efficacy and low hazards to non-target passerines of a single Zn 3P 2 baiting to control vole populations in alfalfa.