Trees—protecting from rodent damage
Voles, mice and rabbit damage can be detrimental to trees and shrubs. Subsurface damage is often caused by voles, which feed on the roots and bark of trees and shrubs. Mice feed on saplings and shrubs below the snow and within the grass layer. Rabbits assault bark and tender buds on areas higher up than the reach of voles and mice.
Protect trunks by placing a cylinder of ¼" (or smaller) mesh, hardware cloth. Or put plastic drainpipe around the trunk. The guards should extend two inches below the soil line (as long as they don't damage roots). Place 18 to 24 inches above the anticipated snow line. Guards should be removed or reinstalled each spring to prevent girdling.
The most effective repellants for rodents contain thiram, a fungicide that is distasteful, yet unharmful, to rodents. Thiram is a water-soluble spray or paint. Apply it with a surfactant. One application is usually enough for the entire dormant season. Apply multiple applications during the growing season.
Discourage rodents by reducing grasses and other vegetation that pests use for cover from predators. Mow or chemically control grasses within a 4' diameter circle around trees. Also, discourage rabbits by reducing vegetative cover, brush piles and other hiding places.
Hunting and trapping, although labor intensive, can be effective. However, mice and vole populations usually don't respond well to trapping or other extermination, such as rodenticides. High reproductive rates draw in pests from surrounding areas. They take advantage of abundant food and habitat following local extermination. Fumigants and electromagnetic or ultrasonic devices are not effective for long-term control of rodents.
For more information, contact the Department of Forest Resources Extension and Outreach office at 612-624-3020.