UMass Extension Greenhouse Crops and Floriculture Program

Preventing Rodent Damage to Overwintering Perennials

Growers are advised to protect their perennials from damage caused by rodents now that winter is near. Small animals will invade overwintering structures, eat most perennials and burrow into pots if given the chance. The most likely critter to cause havoc is the meadow vole. The head and body of meadow voles measure 3 to 5" long and the tail is 1½ to 2½" long. They have brown body hairs mixed with black guard hairs; belly hairs tipped gray and small eyes and ears. Meadow voles are active day and night, year-round. They do not hibernate. They feed all winter long on tubers, bulbs, rhizomes, stems, roots, and seeds and occasionally on insects and animal remains. Meadow voles construct many tunnels and surface runways with numerous burrow entrances. These surface runways are the most easily identifiable sign of voles. By the time the runways are noticed, damage is usually done. Voles are prolific breeders. They may breed throughout the year, but most commonly in spring and summer.

To identify animals responsible for damaged plants in your overwintering greenhouses, try using signs. One way is to place some non-toxic bait such as apples out in a problem area and see what kind of damage is done to that bait. The culprit can be identified by the excrement that is left behind. Another way to identify the animal is to capture one, using a small live trap or a mouse snap trap. Good baits include peanut butter-oatmeal mixture or apple slices. Once the animal is identified, control measures can be taken. It should be noted that voles are capable of carrying diseases that affect humans, so be careful and use protective clothing when handling voles.

The first step to prevent damage caused by rodents is to deny them access to your overwintering greenhouses. Make them rodent tight. Use fine mesh screen wire such as hardware cloth around the perimeter of the greenhouse. Bury it under ground and bend it outward at a 90 angle leaving it at least 6" deep.

Next, mow and clean up the natural vegetation close around the greenhouses to eliminate protected areas for rodents. Most of our wildlife animals will not venture across a wide-open space because they are much more vulnerable to natural predators.

Trapping is not effective for controlling large vole populations, but can be used to control small populations. Place mouse snap traps containing bait perpendicular to the runways.

Chemical repellants are available that can be used on plants. Some repel by giving off an offensive odor and others are taste repellants. These products reportedly work for a number of animal pests. Some of these products may not be persistent and some are easily washed off and need to be reapplied.

Finally, when all else fails, there are toxic baits that are effective for reducing the population. One of the most effective and common baits is zinc phosphide treated, cracked corn, or oats. It is a single-dose toxicant available in pelleted and grain bait formulations and as a concentrate. Anti-coagulant baits are also effective in controlling voles. Anticoagulants are slow acting toxicants requiring from 5-15 days to take effect. Multiple feedings are needed for most anti-coagulants to be effective. Toxic baits can be harmful to children, pets and wildlife and should be used with utmost caution. Read and carefully follow the directions and safety precautions on the label of any of these products.

References

  • Harding, J. 1979. An animal damage identification guide for Massachusetts. pp 62-66.
  • O’Brien, J. M. 1994. Voles. Prevention and control of wildlife damage. Nevada Department of Agriculture. Reno, NV.
  • tockdale, T. 1983. Rodent problems in perennial production. Proc. Herbaceous Perennial Symposium. pp 49-52.
Tina M. Smith
Extension Greenhouse Crops and Floriculture Program
University of Massachusetts, Amherst, MA