Pre-baiting for increased acceptance of zinc phosphide baits by voles: an assessment technique

During a product-performance test of 2% zinc phosphide (Zn₃P₂) steam-rolled-oat groats (11.2 kg ha⁻¹) to control voles (Microtus spp) in alfalfa (Medicago sativa), randomly located, brushed-dirt plots were used to assess broadcast distribution and removal/acceptance of placebo particles. Results showed that the Spyker® Model-75 Spreaders were calibrated adequately, with placebo baits broadcast uniformly onto plots [x ± SD = 3.5 (±2.7) groats 930 cm⁻¹]. Acceptance of the placebos by voles increased rapidly – 28% and 60% by 24 h and 48 h post-broadcast, respectively. Analyses of variance confirmed the uniformity (non-significance) of particles broadcast among enclosures/plots and the significantly greater removal/acceptance of placebos across days. This technique affords an objective decision-making tool for applicators and researchers applying Zn₃P₂ baits in field situations – an objective technique of assessing pre-bait acceptance that should improve efficacy of the rodenticide. © 1999 Society of Chemical Industry