Thursday, May 26, 2016

Voles by Jo Smith

When the snow melts in the spring, you may notice tunneling throughout your lawn and damage to the bark of your trees and shrubs. This damage is likely caused by voles. 

Voles are rodents similar to deer mice but stockier with short tails. They are 4-8 inches long and vary in color from brown to gray. There are three common types of voles in the Yampa Valley:  the montane vole, the long-tailed vole and the western heather vole.  Voles eat a variety of grasses, herbs, and crops. They eat bark on trees and shrubs, especially during the winter months. Voles do not hibernate. They are active day and night, constructing surface runways and underground tunnels with many burrow entrances. During the winter, the burrows are protected by snow.

Voles have an amazing ability to reproduce. They have 3-6 young per litter and 3-12 litters per year breeding year round. Female voles become pregnant at 3 weeks of age. Vole population numbers generally peak every 3-5 years and it seems 2016 is a peak year.  Although voles are prey for foxes, coyotes, bobcats, weasels, snakes, owls and hawks, they reproduce so successfully, predators have little impact on vole populations.

Vole control and eradication is challenging. Voles are classified as non-game wildlife in Colorado and can be captured or killed if they create a nuisance or cause property damage.  Methods to prevent and control vole damage include habitat modification, exclusion, repellents, trapping and poisons. You may need to use multiple strategies to control the voles on your property.

Reducing the amount of available habitat for voles will reduce their numbers. Eliminate weed ground cover and tall grasses by frequent and close mowing. Plant short grasses that do not mat, such as buffalo grass, blue grama or dwarf fescue. Remove summer vegetation around tree trunks (2 foot radius) as voles avoid exposed areas. Damage to lawns can be reduced by close mowing in the fall and removing tall grassy cover near lawns. Crown vetch, a legume unpalatable by voles, may be used as a ground cover or border to discourage voles.

To protect trees and shrubs, wire or plastic-mesh cylinders deter voles. The barriers should project 18 inches above ground and 3-6 inches below the surface. Likewise, raised beds can be lined with ¼ inch mesh hardware cloth to eliminate tunneling into the area.

There are few effective repellents available to protect trees, shrubs and vegetable crops from voles. Little data is available on the effectiveness of these repellents. ThiramTM is manufactured and sold under various trade names. It is labeled for protecting tree seedling, shrubs, ornamental plantings, and fruit trees from voles. Capsaicin (the chemical in spicy pepper) can also be used.  Be sure to follow manufacturers’ precautions before applying these products. Hot pepper sprays are used by some gardeners to ward off voles in vegetable gardens before edible portions and/or heads begin to form.  Homemade repellent recipes are available online.

Voles can be trapped using mouse snap traps. Traps baited with peanut butter and rolled oats or Granny Smith apples work well. Place the traps perpendicular to the runways at nighttime to capture voles heading into and out of their burrows. 

Poison grain baits containing zinc phosphate are used as a short-term solution for vole control. Zinc phosphide (restricted use, most people can not acquire it) is very toxic and extreme care must be taken to avoid risks to children, pets, and non- target wildlife.

For more information about voles in Colorado, visit the Colorado State University Managing Voles in Colorado Fact Sheet (No. 6.507). Good luck vacating your voles.

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