Rodents


Voles

The two common species of voles present in the B.C. Interior are stout-bodied, short-tailed rodents often mistakenly called field or meadow mice.

The meadow vole is about 14 to 17.5 cm long with small eyes and ears that barely extend beyond the fur. The tail is about 1/3 the length of the head and body. The tail, body and head are uniformly covered in a grizzled grey to grizzled brown fur.

The montane vole (mountain vole) closely resembles the meadow vole. It measures13.5 to 16.5 cm long; however, unlike the meadow vole, the tail is less than 1/3 the length of the head and body. Another difference is the underside of the body is grey in the summer and white in winter.

Both species prefer a habitat with abundant ground cover. They usually establish a system of surface runways and underground tunnels. Voles begin feeding on fruit trees when cool weather reduces their summer food supply. Injury to trees can begin in late summer and continue through fall and winter. Complete girdling of the trunk or roots will kill the trees. Damage to roots is often worse than visible damage above the ground.

Cultural Control

1.  Mow the cover crop and remove prunings, tall weeds and grasses to discourage mice from breeding within the orchards.

2.  Remove brush piles and other trash adjacent to orchards to discourage mice from migrating into the orchards.

3.  Destroy all vegetation at the base of trees with herbicides or by cultivation to discourage voles from feeding on the bark. However, retain vegetation where snow cover may be inadequate to protect trees from cold temperature change.

4.  Place wire or plastic mouse guards around the base of trees, especially young trees, to exclude mice. Mouse guards should extend to at least 45 cm above soil level and 5 - 10 cm below.

Rodenticides

Recommended commercial vole rodenticides are formulated as solid bait (i.e. meal bait, pellets, ready-to-use place packs, and paraffin blocks) which should only be placed in burrows or in tamper-proof bait stations to prevent access to the products by children. pets, livestock and non-target wildlife. Bait stations will also protect the contents from moisture deterioration. For voles the best time to set out bait stations is just prior to the first snow fall. Check the bait stations regularly to monitor the disappearance of bait which will indicate if voles are still present. Construct bait stations from old fluming, metal or plastic pipe or pieces of wood. Instructions on using ABS pipe are posted at http://www.publichealth.lacounty.gov/eh/docs/Specialized/Vector_Management/plastic_Pipe.pdf. Place bait stations in areas where voles were evident during the summer or are likely to be found during the winter; e.g., near trees, fences and brush piles. It is important to alternate use of rodenticide active ingredients to prevent rodents from developing bait shyness

The following active ingredients are registered for control of rodents and examples of product trade names of a few are listed in the table at the end of this chapter. Before selecting a rodenticide, check the label to ensure the target rodent is on the label as many are registered only for mice and rat control. Always dispose of dead rodents in garbage or by burying.

1.  Chlorophacinone N is a multiple-dose anticoagulant rodenticide available as paraffinized pellet baits for control of voles, mice, Norway and roof rats, Northern pocket gopher and ground squirrels. Apply a ready-to-use 0.005% bait product in recommended tamper-proof stations or directly into burrows following label instructions.

2. Diphacinone is an anti-coagulant rodenticide available in paraffinized ready-to-use 0.005% pelletizied baits for control of voles or ground squirrels depending on product. Several products are available for control of rats and mice only. The bait is either scattered amongst ground vegetation, placed in burrows or in bait stations, depending on product.

3.  Zinc phosphide N is an acute-poisoning rodenticide available in 2% cracked corn or pellet bait formulations for control of voles, Northern pocket gopher and ground squirrels. The bait releases toxic phosphine gas in the presence of moisture. Apply using burrow building machines or by hand application using hand probes following label instructions.

4. Strychnine is another acute-poisoning rodenticide available as a ready-to-use 0.4% dry bait for control of Northern pocket gopher and ground squirrels. Apply using burrow building machines, secure bait stations, or by hand application using hand probes following label instructions. It is important to remove and bury any dead rodents because they can pose a poisoning threat to predatory animals.

Northern Pocket Gopher

The Northern pocket gopher (often mistakenly called a mole) is a burrowing rodent about 17.5 to 22 cm long. The head is broad with small eyes; its short ears barely extend beyond the fur. The body is narrow and thinly covered in brownish-grey fur except for the lighter underside with some white on the throat, chin and chest. The tail is about half the length of the body. The northern pocket gopher has noticeable sharply pointed, curved claws on its feet with which it digs its underground burrows throughout the year. As it burrows it pushes up small mounds of excavated soil. They can cause severe damage to fruit trees by feeding on roots, often killing young trees.

To avoid pocket gopher damage to replanted trees, apply one or more of the following control methods to rid the property of the pest before or at the time of replanting. Closely monitor for activity by checking for fresh push-ups, especially along borders adjacent to infested lands.

Hand-Probes

Use a hand-probe when infestation is light or as a cleanup operation between burrow-builder treatments. Probe opposite and about 30 cm from the V-shaped indentation of the side of a mound. The probe will drop about 5 - 10 cm when a burrow has been located. Leave probed hole open after baiting. For information on the design and use of hand probes, refer to the fact sheet “Design and Use of Home-Made Hand Probe”, available from the Kelowna BCMA office or downlaod a copy from http://www.agf.gov.bc.ca/cropprot/handprobe.pdf.

Place the required amount of rodenticide bait in the borrow as per label instructions. Make 2-3 bait placements per burrow. Bury dead anilamls and spilled bait found on the soil surface immediately. Maintain a constant supply of bait in the burrow system for as long as there is pocket gopher activity. Do not apply bait on the soil surface.

Burrow-Builders

To build a proper burrow the soil must be damp and the Burrow Builder must be clean before using. Use a broomstick or iron bar, probe gopher runways bar to determine depth of the gopher runway. Set machine to the same depth. Make artificial runways 7 m to 10 m apart encompassing the total infested area and then cross the ends. Apply a rodenticide bait as per label instructions. Immediately after application, use a harrow or similar implement to level mounds in order to monitor for new mounds. Check treated area 10 days after application for new mounds. Any remaing active mounds should be treated again using a hand probe or burrow builder to achieve maximum control. Repeat applications may be necessary. Treating field margins may prevent or slow re-invasion. A detailed description on using burrow builders for pocket gopher control is posted at http://extensionpublications.unl.edu/assets/pdf/g2035.pdf

Traps

Use pocket gopher traps (e.g. Guardian, Victor or Woodstream) where infestations are light or in areas where poisons cannot be used. Begin trapping in the spring when gophers are most active.  It is important to correctly place the tunnel traps in main tunnels. Open the tunnel using a hand trowel or other small shovel and place two traps facing in opposite directions to intercept gophers in both directions. Use wire or light chain to secure the trap to a stake to allow safe and easy removal of the carcass or trap. Make sure the opening is sealed to prevent light or air currents entering the tunnel. Check the trap once or twice daily. If no gophers are trapped after 3-4 days, relocate to another main tunnel. Always be vigilant for gophers invading from bordering properties and act promptly to prevent establishment.

Bait Stations

Place the recommended amount of bait deep in each opened burrow in such a manner that the bait is not visible from the surface. Close the burrow without burying or covering the bait and repeat treatment of any opened burrows after one week.

For above-ground use, place bait in a tamper resistant bait station and replenish baits as necessary. Remove and bury any dead animals because they can present a significant poisoning hazard to predatory animals. Do not place bait above ground exposed to non-target species unless it is in a tamper resistant bait station.

Columbian Ground Squirrel  

The Columbia ground squirrel is a small rodent that burrows in the soil to nest and hibernate, creating mounds of soil next to the borrow opening. They prefer to burrow in banks, hillsides and sloping round and open areas free of dense tree cover. They avoid soils with a high water table.

Adults weigh about 0.4 kg with a body length of 25-30 cm and have a 7.5-12.5 cm long somewhat bushy tail. Reddish-brown fur covers the nose, forelegs and hindquarters, and a mixture of gray and brown fur covers the back and tops of the legs.

Columbia ground squirrels emerge from hibernation in March and April, the males emerging 1-2 weeks earlier than the females. Females mate soon after emerging and produce a single litter of four to five young which do not emerge to feed on nearby host plants for about 4 weeks. They are active until August when they line their nests below the frost line with grass in which to hibernate.

They feed on a wide variety of vegetation, preferring the most succulent species available over the summer.  Most of their water is obtained from all parts of plants. They do not store food but must consume enough to build up enough fat reserves to get them through their winter hibernation (usually 6-7 months each year).

Ground squirrels damage fruit trees by gnawing bark, girdling trunks, eating twigs and leaves, and burrowing around roots. Borrows around the tree base can damage and dry out roots, and make the trees more susceptible to toppling in high wind gusts. Their dirt mounds can make it difficult to mow and can damage equipment.

Ground squirrels are fed upon by many predators (coyotes, fox, weasels, owls, hawks, eagles, badgers, skunks and snakes) which can help to reduce damage along with other management tactics.

Options for ground squirrel control include trapping using spring-loaded leg-hold or body traps, or placing rodenticide products containing 0.005% chorophacinone or 2% zinc phosphide in burrows (hand-baiting) or in covered weather-tight bait stations. See discussion on use of rodenticides, hand probes (hand-baiting) and bait stations under Pocket Gopher control above..

Maintain an uninterrupted supply of rodenticide for 3 weeks or until no further signs of damage or burrow hills are noticed. Visit traps and baited borrows and stations every 48 hours to re-bait if necessary and remove and bury any carcasses which are found above ground.

Always read the product labels carefully before applying any rodenticide products. 

Summary of Registered Uses of Recommended Rodenticides

Product

Active Ingredient

Voles

Pocket

Gopher

Ground

Squirrel

Roof Rat

Burrow Oat Bait

Zinc phosphide

 

 

Rodent Pellets

Zinc phosphide

Rodent Bait

Zinc phosphide

ZP Rodent Bait

Zinc phosphide

Ground Force Pellets

Chlorophacinone

 

Rozol RTU

Chlorophacinone

 

 

Rozol Paraffinized Pellets

Chlorophacinone

 

Pocket Gopher Bait

Chlorophacinone

 

 

Gopher Doom

Chlorophacinone

Ramik Green

Diphacinone

   

Ramik Brown

Diphacinone

     

Gopher-Kil Bait

Strychnine