By Martin Guerena
NCAT Agriculture Specialist
Published December 2018
Field identification of rodents. Photo: Wikimedia Commons
Rats, mice, and voles are some of the most damaging rodent pests worldwide. They destroy crops in the field and in storage; contaminate food, seeds, produce, and fruits; and transmit numerous diseases. These rodents also cause tremendous damage to infrastructure and structural damage to buildings. It is important to identify the exact type of rodent that is causing problems in order to apply the correct control strategies.
Vole. Photo: Flickr
The two most important rat species are roof rat (Rattus rattus) and Norway rat (Rattus norvegicus). The most common house mouse species is Mus musculus, and voles or field mice number in the hundreds of species. To determine which of these rodents are responsible for damage at your farm or home, look for the following signs:
Clockwise from the top are Norway rat, American cockroach, and mouse droppings. Photo: Flickr
Successful management of rats, mice, and voles is a continuous commitment utilizing more than one control method. Complete control is not always possible because of area-wide activities over which you have very little control, such as neglected structures nearby, abandoned fields, lack of predators, improper garbage disposal, and overgrown vegetation.
Habitat Modification. Many rodent problems can be minimized by making the farm and areas around buildings less hospitable to rodents through removal of shelter and potential food and water. Remove debris including rocks, wood, and brush piles that can provide shelter for burrow entrances of the Norway rat and voles. Keep ground vegetation around buildings clear, and trim the bottoms of hedges and other landscape plants up from the ground. Trim trees that overhang buildings back at least six feet. Avoid ivy, or any ground cover that would screen rats' activities. If you have fruit or nut trees, make sure you pick up whatever falls on the ground. Store equipment, firewood, and other materials off the ground on pallets and away from building walls and fences. Clearing grassy areas and weeds will discourage voles by reducing their food and exposing them to predators and environmental stress.
Exclusion. In buildings, it is easier to keep rodents out than to get them out once they are inside. Seal, or screen with mesh wire, any opening larger than 1/4 inch, such as openings for water pipes, electrical and other utility cables, and vents. Sewer lines can have cleanouts that may provide access to rats, which can then get into the building. Materials used to restrict access include sheet metal to prevent climbing and gnawing, wire screen, steel wool, mortar, and concrete patches. Areas to inspect and use these materials include gaps or openings in roof tiles, roof vents, attic vents, gaps under entry doors, gaps around chimneys, crawl space covers, gaps under metal flashing, and heater or air-conditioning vents. Other preventative practices include clearing wood piles from the building, keeping storage sheds and animal hutches clean, trimming tree limbs near roofs, rodent-proofing the bird feeder, feeding pets periodically so there is no leftover pet food in the dish, and keeping trash containers sealed and away from the building. On farms, it is a bigger challenge because you are dealing with building structures, crops, animal facilities, and feed storage. Sanitation around the barn is critical: remove spilled feed, piled boxes, or anything rodents can hide in; block off entrances; and get rid of nesting materials. Remove food and water sources and keep feed in covered hoppers.
Baiting. The use of toxic baits can pose threats to wildlife, pets, and children, so they should be used with extreme caution. Baits accepted in certified organic production will be mentioned in this publication. For conventional baits, such as strychnine and anti-coagulants, consult your local Extension website for guidance and always read the label of all pesticides.
Snap trap. Photo: Wikipedia
Trapping. Trapping is an effective method of control for small areas or light infestations. Snap traps are very effective, inexpensive, and may require more labor, but are considered to be more humane because they generally kill the rodent instantly. Baiting the traps with peanut butter, dried fruit or nuts, or dried pet food may be necessary to lure the rodent to the traps. It's good practice to tie the traps down (using twine, tying to a nearby pipe or beam, which will prevent too much movement of the trap) because you don't want a wounded rodent dragging a trap to areas that you can't access. Voles seldom wander from their runways and paths, so setting traps without bait at right angles in front of burrow entrances and paths can be effective. Norway rats travel along edges of buildings or against walls, so place the triggers against the walls and at entrances to a structure, where the rodent is forced through a narrow opening. Roof rats travel up beams, rafters, trees, and ledges, where traps can be fastened securely. If using snap traps outside, a trapping box may be necessary to protect non-target wildlife, pets, and children. Check traps daily to remove dead rodents and reset sprung traps quickly to prevent trap and bait shyness. Use gloves or plastic bags to remove dead rodents because they may carry diseases.
Glue boards work like flypaper, trapping the rodent as it attempts to cross the board. With these types of traps, the rodent may not die quickly and you may need to kill it. Glue boards also lose their effectiveness in areas with high dust, debris, and temperatures.
Electronic traps kill rats by electrocuting them with high-power batteries. They catch one rat at a time and are expensive compared to snap traps. The traps are convenient in some situations, especially with individuals who are squeamish about cleaning snap traps for reuse. The electrocuted rat slides out of the trap with minimal handling when the trap is emptied.
Live traps may be used but are not recommended because the rodents will have to be killed or released elsewhere. Releasing rodents to other areas may be illegal and will just transfer the problem to other areas. Releasing to wild areas will be disruptive to the natural ecosystem, and rats, especially, are known to decimate bird and reptile populations.
Domestic cats can help keep rat, mice, and vole populations down. Photo: Martin Guerena, NCAT
Predators and Natural Control. Depending on the wildlife that lives in your region, many types of predators may be able to help reduce rodent populations. A healthy population of wild predators may include bobcats, foxes, coyotes, badgers, skunks, weasels, snakes, owls, ravens, hawks, and most other large birds of prey. Predation accounts for a large proportion of rodent mortalities, though it will not completely control a population.
It is, nonetheless, worthwhile to encourage predation—especially through the use of raptor (hawk and owl) platforms, nest boxes, and perches throughout the farm. Research has demonstrated that by attracting raptors to agricultural areas, pesticide use decreases (Lindell et al., 2018; Novak and Torfeh, 2017). USDA's Natural Resources Conservation Service (NRCS) has funding to help farmers install wildlife structures on their land, as well as funding for many other conservation practices. Your local USDA Service Center can be located online here.
Lindell, C., R.A. Eaton, P.H. Howard, S.M. Roels, and M.E. Shave. 2018. Enhancing agricultural landscapes to increase crop pest reduction by vertebrates. Agriculture, Ecosystems and Environment. April 1. p. 1-11.
Novak, K. and D. Torfeh. 2017. Raptor Pilot Study for Levee Protection. Ventura County Public Works Agency Watershed Protection District.
Barn Owls in Integrated Pest Management and Sustainable Agriculture. 2017. By Barn Owl Box Company.
Farmscaping to Enhance Biological Control. 2000. By NCAT/ATTRA.
How to Identify and Get Rid of Mice. 2018. By The Old Farmer's Almanac.
How to Identify and Get Rid of Voles. 2018. By The Old Farmer's Almanac.
IPM Action Plan for Rodents. 2018. By eXtension.
Organic IPM Field Guide. 2006. By NCAT/ATTRA.
Pest of Homes, Structures, People, and Pets: Rats. 2011. By University of California Statewide Integrated Pest Management Program.
Voles: Learn about vole biology, food habits, damage caused by voles, and damage control methods. 2018. By Penn State Extension.
Rats, Mice, and Voles: Vertebrate IPM Tip Sheet
By Martin Guerena, NCAT Agriculture Specialist
Published December 2018
Tracy Mumma, Editor
Amy Smith, Production
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This page was last updated on: April 30, 2019