MANAGING RABBIT AND VOLE PROBLEMS IN KENTUCKY ORCHARDS
Thomas G. Barnes, Extension Wildlife Specialist
Voles (Microtus spp.) and cottontail
rabbits (Sylvilagus floridanus) may cause extensive damage to orchards
by girdling seedling and mature trees. The amount and extent of damage
will vary, and the best approach is a pest management system that integrates
biological, mechanical, and chemical prevention and control techniques.
Animal Facts and Biology
Often referred to as meadow or field
mice, voles are small compact mammals with stocky bodies, small rounded
ears, short legs, and a short tail. When fully grown, voles are 4 to 5
inches long. Their long, coarse hair can be blackish, grizzled, or reddish.
The three vole species that damage
Kentucky orchard trees are pine voles (Microtus pinetorum), prairie
voles (Microtus ochrogaster), and meadow voles (Microtus pennsylvanicus).
Identification of individual species is essential because pine vole damage
occurs below ground.
Voles eat a variety of grasses and
broad-leaved weeds. They will also eat seeds, tubers, bulbs, and rhizomes.
Prairie and meadow voles feed on tree bark primarily during the fail and
winter. However, pine voles characteristically attack trees of all sizes
during all seasons. Most pine vole damage occurs below ground where the
animals feed on rootlets and the bark of larger roots.
Voles do not hibernate and are active
all year long. They are most active during the day. Areas of activity are
small (1/4 acre) and depend on population number, food supply, habitat,
and season. A typical vole habitat consists of heavy, dense ground cover
where the animals construct many burrows, tunnels, and runways. A single
burrow system may contain several adults and young.
Voles breed from January through October
in Kentucky and can produce an entirely new generation within about 60
days. Vole numbers fluctuate from year to year; under favorable conditions,
populations can increase rapidly. Most orchard problems occur during these
periods of rapid population growth.
Although voles have a high reproductive
rate, they are also a mainstay in the diet of hawks, owls, foxes, coyotes,
and other meat-eating animals. In addition, the lifespan of a vole is short,
ranging from 2 to 16 months. More than 80% of young voles die in their
first month of life.
Our most abundant and common rabbit
is the eastern cottontail. The cottontail rabbit is often grouped with
the rodents (mice, squirrels, rats) because of its large, prominent front
teeth. However, rabbits have a second, smaller set of teeth directly behind
the first set, a characteristic which places them in the group Lagomorphs.
Typical eastern cottontail rabbits
weigh between 2 and 4 pounds and are 15 to 19 inches long. Cottontails
appear gray to brownish gray with a short tail and big ears. The underside
of the tail is white and looks like a cotton ball. Hence the name cottontail.
Rabbits will devour a wide variety
of green vegetation. A rabbit's appetite varies considerably with season
and locality. During the winter, rabbits appear to prefer the bark of apple
trees, black and red raspberries, and blackberries. Clovers, grass, and
broad-leaved weeds are a mainstay in summer diets. Cottontails usually
prefer to feed at night although they are also active during daylight hours.
Rabbits tend to concentrate in favorable
habitats around a brushy fencerow, brush or junk piles, upland thickets,
or field edges. Their travels usually do not exceed 10 acres. Population
levels are directly linked to the quantity and quality of habitat present.
The lifespan of a cottontail is short
(12 to 15 months); however, cottontails have an extremely high reproductive
potential. Kentucky cottontails may have 3 to 8 young per litter and up
to 4 litters per year. The first litter usually appears in March.
Fortunately, this high reproductive
potential is not reached because cottontails also have a high death rate.
Cottontails, like voles, are a mainstay in the diets of most meat-eating
Predation, disease, weather, and encounters
with humans contribute to the annual death rate. Up to 35% of the young
die within the first month, and 65% of the remaining animals will die over
Most damage to orchard trees occurs
during the winter when other preferred food supplies have dwindled and
the animals resort to gnawing on tree bark. Because of the cottontail's
high reproductive rate, control is sometimes necessary to reduce damage.
However, complete eradication or extermination is not possible, necessary,
or even desirable because of the cottontail's status as a preferred game
species. Before attempting to prevent or control damage occurring to orchard
trees, be sure to correctly identify the culprits responsible because control
techniques vary by species. Correct identification is relatively easy based
upon evidence at the site of damage.
Girdling and gnaw marks do not necessarily
indicate vole damage because cottontail damage can look similar. However,
the presence of tracks, droppings, and burrow systems should verify initial
observations. Typical vole damage can be differentiated from rabbit damage
by the lack of uniformity of gnawing marks and the area of tree damage.
Gnawing marks from voles usually occur at or below the surface at various
angles and in irregular patches. The gnawed patches are approximately 1/8
inch wide, 3/8 inch long, and 1/16 inch deep.
Rabbits, on the other hand, clip tender
young shoots and terminal buds as well as gnawing on the trunk. The gnawing
marks are larger and appear as clean, knife-like cuts at a 45-degree angle.
Rabbit tracks and round droppings are also quite distinctive.
Prevention and Control
An orchard owner should pursue four
general steps when developing a successful integrated pest management system.
1.Correctly identifying the animal
species causing the problem.
2.Modifying the habitat to make it
less attractive to the problem animals.
3.Using environmentally sound prevention
and control techniques appropriate for each individual situation.
4.Monitoring and evaluating the area
for signs of reinfestation to determine if the control worked or if additional
control is necessary.
The best approach to managing vole and
rabbit damage in orchards is to use an integrated system with a variety
of techniques. Not all techniques work in every situation, and orchard
owners must be willing to use different approaches for their individual
problem. Often a combination of techniques produces the best results. Control
works best during the winter, reducing next year's breeding population.
Habitat modification and exclusion provide the best long-term control for
both voles and cottontails.
The various prevention and control
techniques may be grouped as (1) biological, (2)mechanical, or (3) chemical.
Each technique has advantages and disadvantages depending on management
objectives, expense, location, and situation. The options for preventing
and controlling voles and cottontails in orchards are discussed below.
The three types of biological control
are habitat modification, population reduction through hunting or trapping,
and installation of raptor perches.
Habitat modification is particularly
effective in deterring voles and rabbits. Dense, heavy vegetative cover,
mulch, and weeds provide optimum habitat for voles and rabbits by providing
food and protection from predators. If you remove this food and cover source,
the area will provide less suitable habitat. If mulch is used in the orchard,
it should be placed no closer than 3 feet to the trees. Vegetation remaining
between rows should be mowed regularly.
Soil tillage is particularly effective
because it eliminates any cover, destroys existing burrow systems, and
kills a percentage of the vole population. Brush piles, weed patches, junk
dumps, and stone piles in or adjacent to the orchard should be removed,
thereby eliminating places where rabbits live and hide. This method of
control is one of the most effective, long-term solutions in reducing vole
and rabbit damage to orchard trees. It has several advantages over other
techniques because it is economical, does not place harmful chemicals into
the environment, and is a long-term solution to the problem, not a quick
Hunting rabbits in rural areas is a
quick, easy, and effective method of control. Cottontails, avidly pursued
by hunters, are legal game animals in the Commonwealth of Kentucky. A permit
must be obtained from your county conservation officer to destroy cottontails
anytime except during the legal hunting season. During hunting season you
must have a valid Kentucky hunting license to shoot cottontails.
You must be persistent if hunting is
your sole method of control. Removing rabbits in one year does not guarantee
rabbit populations will remain low because of the rabbit's high reproductive
potential. The best results can be achieved by hunting in the early morning
or evening when the rabbits are most active. By permitting hunting, orchard
owners provide public access to a public resource while reducing damage
Trapping is not effective in reducing
large vole or rabbit populations because time and labor costs are prohibitive.
However, small populations can be controlled by trapping. Live trapping
is the most effective way to remove cottontail rabbits. There are a variety
of commercial live traps available at hardware, agricultural supply and
feed stores, or sporting goods stores. Live traps are more effective if
you cover them with canvas or some other dark material.
Rabbit traps can be baited with cob
corn, oats, or dried apples during the fall and winter. Placing rabbit
droppings inside the trap may make it more effective. Place the traps in
areas where cottontails have been feeding or resting close to suitable
cover. Bait the trap and wire the door open for several days. Once the
bait is being taken regularly, remove the wire and set the trap. You must
check the traps daily and remove captured animals. If the trap fails to
catch any cottontails within a week, move the trap to a different location.
When vole populations are low or concentrated,
trapping may be an effective control technique. The simple, wooden snap
trap or Sherman live trap is commonly used. Bait the traps with a mixture
of peanut butter and oatmeal or dried apples. Trap placement is crucial
as voles rarely stray from their usual travel routes. Examine the area
for nests, burrows, and runways in the grass or mulch. Place the traps
perpendicular to the runway with the trigger end in the runway. Be sure
to set enough traps (remember a vole's territory is about 1/4 acre). Fifty
to 100 traps should be sufficient in many small orchards. Traps must be
checked daily and dead animals removed.
One final biological method of reducing
vole and rabbit populations is to install raptor perches. These structures
provide hawks, owls, and other birds of prey an elevated "overlook" where
they stand waiting to catch small animals. One perch per acre or two, located
on higher ground, should be sufficient. While predators alone do not control
vole or rabbit numbers, installation of raptor perches may help keep populations
low once they have been reduced through alternative techniques.
The most effective mechanical control
methods are those which prevent animals from entering the general area
(fencing) or preventing individual trees from being clipped. While fencing
is the best way to eliminate animal damage, the cost of constructing effective
fences is often prohibitive. Examine costs and benefits carefully before
investing in this option. Even though fences may seem costly, with proper
care they provide relief and protection from damage for many years.
Rabbit- and vole-proof fences are easily
constructed of 1-inch mesh netting woven or poultry wire. The fence should
stand 30 to 36 inches high. The bottom 6 inches should be turned outward
and buried at least 6 inches under the surface. The lower 2 feet of the
fence should be covered with a small (1/4 inch) mesh wire or hardware cloth
to prohibit voles from entering. Be sure to keep 6 inches of this below
ground to prevent voles from burrowing under it. Inexpensive chicken wire
fences can also be constructed to exclude rabbits; however, this fencing
will require periodic replacement.
In most situations, protecting individual
trees is more practical than excluding animals from the entire orchard.
Plastic or 1/4 inch hardware cloth cylinders, 18-24 inches high and 4 inches
under the surface, can be placed around individual trees. For adequate
protection, these cylinders should be braced away from the trunk to prevent
cottontails from pressing them against the tree and gnawing through them.
There are a variety of commercial plastic, metal, or nylon tree guard tubes
and wrappings available. Contact your local garden center or agricultural
supply store for materials available in your area.
The two main groups of chemicals used
to prevent or control rabbit and voles are repellents and toxicants. Repellents
work well in reducing cottontail damage, however, their effectiveness in
reducing vole damage has not been demonstrated. There are no toxicants
(poisons) registered for use against rabbits, however, toxicants have been
a mainstay in controlling vole damage.
Chemical repellents are classified
as either contact or area. Contact repellents are applied directly to plants
and repel by unpleasant taste, whereas area repellents are applied next
to plants and repel by smell alone. Area repellents may be slightly less
effective than contact repellents. It is important to recognize that repellents
will not eliminate damage. They only reduce the severity of browsing.
Repellents should be applied before
damage occurs and must be reapplied frequently after a rain, heavy dew,
or new plant growth. Always follow label directions for the repellent you
are using. Never apply repellents to any portion of a plant likely to be
eaten by humans unless the label permits it.
There are a variety of commercially
available chemical repellents on the market today. During the dormant season
apply contact repellents when temperatures are above freezing.If you have
rabbit problems during the growing season apply a contact repellent at
about half the recommended concentration. Commercially available repellents
can be found under a variety of trade names, and the active ingredient
is usually bone tar oil, thiram, fermented egg solids, or ammonium soaps
of fatty acids.
Be imaginative in your approach to
using repellents. For example, placing several handfuls of human hair in
a mesh bag and allowing it to blow in the breeze may be effective. Some
people have successfully used hot pepper sauce to make trees distasteful
to animals. You can make your own hot sauce repellent by mixing 1 tablespoon
hot sauce in 1 gallon water. Add 2 tablespoons antidesiccant per gallon
to allow the repellent to stick to the bark. Spray the foliage and bark
when temperatures are above 40 degrees F.
A variety of toxicants is registered
for use in controlling vole populations. When using toxicants, take extra
precautions to ensure the safety of children, pets, and nontarget animals.
Follow product label instructions carefully. Never use a pesticide in a
manner inconsistent with its labeling. Failure to comply with directions
provided may subject you to severe sanctions and penalties provided by
state and/or federal laws.
Toxicants designed to kill voles and
mice are called rodenticides. Rodenticides are classified as single-dose
or multiple-dose depending on how long it takes the poison to act.
Single-dose (acute) rodenticides require
only one feeding to be lethal. Multiple-dose (anticoagulant) rodenticides
are slow acting because voles poisoned with anticoagulants die from internal
bleeding. Thus, they must be consumed for several consecutive days to be
effective. They are probably the safest and most preferred type of rodenticide.
Many types and brands of anticoagulant
rodenticides are available on the market today. The most effective and
potent contain cholecalciferol, brodifacoum, bromadiolone, chlorophacinone,
Because voles must feed on the bait
for 3 to 5 days, the bait must be available for an extended period of time.
Be sure to place the bait in runways or next to burrows so voles will find
it during their normal travels.
One method of keeping bait available
in good condition is to establish bait stations. You can purchase commercial
bait stations or make your own from 2- to 3-inch diameter plastic pipe.
Many growers place shingles or boards
in their orchards during September. They visit these stations during October
and inspect them for vole runways beneath the covers. If runways are found,
a rodenticide is placed under the boards. Some growers use machines which
build artificial trails and dispense rodenticide in these trails.
Zinc phosphide is the most commonly
used acute poison. It is a restricted use pesticide. Any person using this
pesticide must be certified by EPA or work directly under the supervision
of a certified person. Place the bait in runways or next to burrows where
voles will find it. To increase the effectiveness of poison grain baits,
prebait with good quality grain for 3 to 5 days. The best time to use grain
baits is during the winter.
One problem with using zinc phosphide
is "bait avoidance or shyness" which occurs when voles eat only enough
to make them sick. If this happens, voles will not eat any bait for 6 months
or more. To avoid this situation, do not use zinc phosphide more often
than every 6 months and always follow label instructions. This rodenticide
also comes as a tracking powder or in paraffin blocks.
Trade names are used for simplicity.
No endorsement is intended, nor is criticism implied of similar products