Abstract

Two new anticoagulants (bromadiolone—90% control) and (difethialone—87% control) gave excellent control of voles in field and laboratory tests. The older anticoagulants, chlorophacinone—84% control and diphacinone—75% control, and two zinc phosphide formulations (Bell Labs—84% control and Hopkins—79% control) also gave excellent field control of voles. The Ridall zinc phosphide formulation—61% control, and cholecalciferol (vitamin D₃)—59% control did not perform as well as the other rodenticides previously mentioned. The antibiotic, oxytetracycline, killed from 40% to 80% of pine and meadow voles in laboratory trials when applied to cut apples, but only 10 to 30% when pelletized baits were presented. In a mixed pine and meadow vole orchard population, zinc phosphide raised the ratio of surviving pine to meadow voles while anticoagulants lowered the ratio. Thus, the rotation of rodenticides is thought to be desirable to prevent the shift of one species to the other in mixed populations and to prevent bait shyness from developing to zinc phosphide.