Bait Stations for Controlling Voles in Apple Orchards

Bait stations made with polyvinylchloride (PVC) pipe were compared with hand-broadcast applications of rodenticides for achieving long-term control of pine and meadow vole populations (Microtus pinetorum and M. pennsylvanicus, respectively) in two apple orchards in the mid-Hudson Valley of New York. The stations were constructed of three pieces of 1.5-in diameter PVC tubing joined together in the shape of an inverted "T". Roofing shingles were placed over the entrances to some of the bait stations to encourage use by voles, while others were left uncovered. All stations were tied to trees, with no attempt to place them near runways or burrow entrances. Both pine and meadow voles consumed bait from the stations, regardless of whether the entrances were covered with roofing shingles. However, plugging of entrances with dirt was prevalent during winter in stations with roofing shingles. Vole activity and capture success were consistently lower on the plots with the two types of bait stations than on either the control or broadcast baiting plots 13, 26, 39, and 52 wk posttreatment, although the differences were not statistically different (p>0.05). The best control was achieved during the winter and early spring. Although spoilage of bait due to high humidity may limit its effectiveness in Eastern New York during the late spring and summer, the inverted "T" bait station provides a practical means of controlling voles in apple orchards during winter and early spring. I/Department of Natural Resources, Cornell University, Hudson Valley Laboratory, Highland, NY 12528 2/NY Cooperative Fish and Wildlife Research Unit, Department of Natural Resources, Cornell University, Ithaca, NY 14853 INTRODUCTION Pine and meadow voles cause substantial economic losses in apple orchards in Eastern New York (Biser 1967, Pearson 1976, Pearson and Forshey 1978, Forshey et al. 1984). By girdling the bark and roots of trees, these rodents kill trees, reduce harvest yields, and increase the time required for new plantings to come into production. Growers employ a combination of cultural and chemical techniques to control vole populations in their orchards (Byers 1985). Regular mowing of the orchard groundcover and maintenance of a vegetation-free zone around the base of trees reduces the carrying capacity of the orchard for voles. Wire-mesh tree guards prevent girdling by meadow voles (Davis 1976), but not pine voles, which cause most of their damage to underground roots. Toxic baits are also an important and necessary component of most successful control programs (Byers and Young 1978). In spite of their widespread use, toxic baits have not always given consistent or satisfactory control. A common problem in the northeastern United States is applying baits at a propitious time; frequent and unpredictable rain and snow storms restrict the effective life span of broadcast baits. Because snowcover and adverse weather likewise often preclude applying baits during the winter, most growers apply them during the autumn after apple harvest. While this strategy reduces pest populations just prior to the onset of winter, new voles often reinvade denuded areas (VanVleck 1968, Miller and Richmond 1984) and inflict substantial damage under the cover of snow, before a grower even realizes that voles have reinvaded his orchard. An effective method of delivering baits to voles during the winter, when most damage occurs and when bait acceptance is likely to be greatest due to the scarcity of