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Vole management for Michigan crop producers

Vole management for Michigan crop producers
Species overview
 
Voles (Microtus sp.) are compact rodents with stocky bodies, short legs and short tails. Their eyes are small and their ears partially hidden. They are typically brown or gray, though many color variations exist. For more information on how to identify rodents, refer to the University of Nebraska Cooperative Extension publication, “Prevention and Control of Wildlife Damage.”
 
Voles occupy a wide variety of habitats. They prefer areas with a heavy ground cover of grasses, grass-like plants or litter. Voles are active day and night and do not hibernate. Based on the particular vole species, they construct either many surface runways or shallow tunnels in dense grass with numerous burrow entrances. In the winter, they are active in runways under the snow. Voles eat a wide variety of plants, most frequently grasses and forbs. In late summer and fall, they store seeds, tubers, bulbs and rhizomes. They eat bark at times, primarily in fall and winter, and will eat crops, especially when their populations are high.
 
Voles are extremely prolific. Their peak breeding activity occurs between March and October, but when winters are mild, voles may breed all year long. A female vole could potentially produce over 70 young in a year. Scientists have found that vole populations expand and contract on a four-year boom-bust cycle. Extensive damage may occur in orchards, particularly during peak population years.
 
Girdling and gnaw marks alone are not necessarily indicative of the presence of voles since other animals, such as rabbits, may cause similar damage. Vole girdling can be differentiated from girdling by other animals by the non-uniform gnaw marks. They occur at various angles and in irregular patches. Marks are about 1/8 inch wide, 3/8 inch long and 1/16 inch or more deep. Rabbit gnaw marks are larger and not distinct. Rabbits neatly clip branches with oblique clean cuts. Examine girdling damage and accompanying signs (feces, tracks and burrow systems) to identify the animal causing the damage.
 
 
Network of vole runways. 
 
The most easily identifiable sign of voles is an extensive surface runway system with numerous burrow openings, which are most visible in spring after snow melt. Runways are 1 to 2 inches wide. Vegetation near well-traveled runways may be clipped close to the ground. Feces and small pieces of vegetation are found in the runways.
 
Management
 
Voles are classified as nongame mammals and can be controlled without a permit when causing damage. Contact the Michigan Department of Natural Resources for details regarding applicable codes and regulations.
 
No single management method to prevent vole damage works all the time or in all settings. Generally, management methods should be combined so that one method enhances the effects of another. Monitoring is critical to minimize vole damage and selecting the correct method of control. Exclusion, environmental modification, repellants, toxicants and trapping may all be considered as methods of control and are typically used in some combination depending on the population size, timing and potential damage.
 
Hardware cloth or plastic cylinders can effectively exclude voles from seedlings and young trees. The mesh should be 0.25 inch or less in size. Bury the wire 6 inches to keep voles from burrowing under the cylinder. Large scale fencing of areas is probably not cost-effective.
 
 
Trees girdled by voles. 
 
Modifying environmental factors to moderate vole populations can be useful. Burning, mowing, using herbicides or planting low growing ground cover to reduce vegetative cover can help make a site less attractive to voles. Controlling ground cover also exposes voles to greater risk of raptors, coyotes and other predators. Removing plant cover surrounding an agricultural area may also help in slowing movement of new voles into a site. You might also consider encouraging raptor predators through perches or nest boxes. Ideally, adjacent landowners can work together to manage large areas of land to prevent high vole populations from becoming established.
 
Repellents are relatively expensive and provide only short-term protection. Precipitation may wash some off. When foods are in short supply, such as in winter, the effectiveness of repellents usually decreases.
 
Using rodenticides is an important component of an integrated vole control program, but it is not a stand-alone control. Voles have a relatively short lifespan and a high rate of reproduction, making lethal control strategies effective for a limited amount of time, further enforcing the need for an integrated approach to control. There are a limited number of rodenticides labeled for use in cropping systems and availability varies by state. Carefully review labels to ensure the site is listed before application. Use rodenticides according to the label.
 
In general, rodenticide application to bearing crops is only permitted during the dormant season. Application to non-food crops is generally less restricted. Many products recommend using bait stations to help protect non-target organisms. Read and follow all label directions to reduce the risk of pesticide exposure to yourself, others, non-target organisms and the environment. Refer to the Michigan State University Extension article, “Rodent control for Michigan fruit, nut and Christmas tree producers” for more information on rodenticides.
 
 
Vole injury on larger roots of an orchard tree. 
 
Trapping is not effective in controlling large vole populations because labor costs become prohibitive. However, mouse snap traps can be used to control a small population. Place the trap perpendicular to the runway with the trigger end in the runway. A peanut butter-oatmeal mixture or apple slices make good baits. Fall and late winter are periods when many vole species are easiest to trap. 
 
Considerations
 
As in most situations with vertebrate pests, a combination of methods may be more effective than relying on any one method for controlling vole damage. Most problems with voles in urban and backyard areas probably involve small populations of voles that can be controlled with habitat modifications, fencing or exclusion, or trapping. Nonurban damage situations may involve larger populations of voles over greater areas, and can be resolved with by habitat modification and toxic baits.
 
Voles don’t always cause significant damage to property. Populations of voles, however, can increase quickly and be cause for concern. Generally, a direct relationship exists between populations of voles and the expected overall level of damage. Before undertaking control, consider the extent of the problem in relation to the cost of control. For example, a few voles could damage a highly valued tree or flower bed and warrant control. At other times, they may go virtually unnoticed, making control unnecessary. Usually, it is more cost-effective to respond quickly to signs of damage than to wait until damage becomes severe. The complete elimination of rodents from ag systems is neither necessary nor feasible.
Source : msu.edu