Check the stations after 24 hours. A record of repeated assessments over a period of months or years gives a more accurate indication of vole activity. These vole monitoring stations can be used later as bait stations. You can get a general estimate of vole activity by looking for vole runways on or just below the ground surface. Voles usually nest near the base of a tree trunk.
Voles tunnel through snow to any depth.
Embed guards at least 2 inches below the surface. Trunk guards do not prevent underground damage by pine voles. Flail and rotary mowers do a much better job than sickle bar mowers at making orchard ground cover less suitable for voles. An herbicide strip to kill vegetation in the tree row, removing brush and weedy areas around the orchard, and removing or mowing dropped apples, are effective ways to reduce or even eliminate meadow voles from the orchard. Removing sucker growth, which attracts voles, will also help.