GOVEl

L'CATIONS

0G7

Strategies

for Reducing
Wildlife Damage
in Orchards

BY ROBERT K. SWIHART
AND MICHAEL R. CONOVER

s

February 1988

Digitized by the Internet Archive

in 2011 with funding from

LYRASIS members and Sloan Foundation

http://www.archive.org/details/strategiesforredOOswih

Strategies for Reducing

Wildlife Damage in Orchards

BY ROBERT K. SWIHART
AND MICHAEL R. CONOVER

Wildlife damage to crops is a major problem
for orchardists in Connecticut. Four species
cause the majority of damage and tree mortality
occurring in Connecticut apple orchards: meadow
voles (Microtus pennsylvanicus), pine voles
(Microtus pinetorum), white-tailed deer
(Odocoileus virginianus), and woodchucks
(Marmota monax). Voles damage trees by
gnawing the roots and main stem. Deer browse
heavily on apple trees, especially dormant twigs
and buds during winter. Woodchucks damage
trees by gnawing and clawing them, and they
dig burrows in orchards, thereby posing a hazard
for both men and machinery. Here, we present
information on the ecology and behavior of
voles, deer, and woodchucks that relates to the
control of damage caused by these species. We
discuss field-tested techniques that orchardists
can use to protect their plants as well as new
methods which show promise.

VOLES

Voles as agricultural pests Two species of
vole, meadow vole and pine vole, have posed
problems in Connecticut orchards for at least
50 years (Merrill, 1939). These rodents damage
fruit trees, primarily apple trees, from late fall
through early spring by gnawing phloem and
cambium tissues on the main stem and large
lateral roots. Vole damage can result in
reduced vigor, lower yields, and higher mortality
of apple trees (Sullivan et al., 1980; Richmond
et al., 1988). Damage by voles can be
extensive, and control is costly. A survey of
American orchardists in 1978 concluded that
123,000 apple trees were killed annually by
voles, 37% of which were of fruit-bearing age
(Ferguson, 1980). In Pennsylvania during the
mid-1970s, growers spent four times more on

control of voles than on deer and birds
combined (Anthony and Fisher, 1977).

Damage by meadow voles is characterized by
girdling and patches of gnaw marks on the stem
close to the ground. Gnaw marks of voles
differ from those of other gnawing animals
(e.g., rabbits) because they are irregular in
appearance, occurring at various angles on the
stem. Individual tooth marks are only about
1/16 inch wide. Damage by pine voles usually
is not visible because it occurs underground.

The success of any control technique will be
determined in part by the ecology and behavior
of the pest species. For example, toxicant-
coated grains often are not consumed by voles,
probably because voles are not particularly fond
of seeds; rather, they are almost entirely
herbivorous (Batzli, 1985). Although meadow
voles and pine voles both feed on apple trees,
differences exist between the species.
Understanding some of the major differences in
their ecology and life history helps explain how
control techniques might affect both species
differently.

Behavior and ecology Meadow voles are
distinguished from pine voles by their larger
size, longer tail, and lighter fur (Figure 1).
Adult meadow voles attain weights of 1.2 to
1.6 oz. The species is prolific even by rodent
standards, with females capable of breeding at
26 days of age, having a gestation period of
only 21 days, and litters most frequently
numbering 5-6 young (Bee et al., 1981; Keller,
1985). Pine voles, in contrast, are considerably
smaller, weighing only 0.6 to 0.9 oz. as adults
(Miller and Getz, 1969). One consequence of
their smaller size is that an adult pine vole
could be expected to consume only about 70% of
the daily food intake of an adult meadow vole.
In addition, pine voles exhibit a lower potential

Connecticut Agricultural Experiment Station

Bulletin 855

for population growth; reproductive maturity of
females is not attained until 33 days of age,
and maturity may occur much later. Gestation
periods (24 days) and litter sizes (2-3) of pine
voles also indicate a reduced reproductive
potential relative to meadow voles (Schadler and
Butterstein, 1979).

Meadow voles travel in orchards through
surface runways, which are built by clipping
vegetation at ground level. These runways are
most visible in early spring after snow melt but
prior to the growth of new vegetation. Pine
voles do not use surface runways; they construct
extensive tunnel systems below the soil surface,
usually within the boundary marked by a tree's
dripline. As a result, damage by pine voles
generally is confined to roots, whereas meadow
voles damage the main stem. Individual voles
typically occupy a "home" area within the
orchard, and although considerable variation
exists regarding the size of home ranges, 0.05
acres is representative for meadow voles
(Swihart et al., 1988). Home ranges of pine
voles are only about one-fifth as large,
averaging 0.01 acres (FitzGerald and Madison,
1983). Although both species will make use of
areas under fruit trees, meadow voles also
occupy the grassy areas between rows, especially
when pine voles are present in the orchard

(Cranford and Derting, 1982). Pine voles may
inhabit deciduous woods, but their numbers in
such areas are low relative to populations in
orchards (Miller and Getz, 1969). Meadow voles,
on the other hand, do not inhabit wooded areas
but are abundant in a number of agricultural
habitats as well as in wet grasslands and
roadsides (Getz, 1985). Because of their more
wide-ranging movements and more general
habitat requirements, meadow voles are more
likely to infest or quickly recolonize an area.

In addition to differences in habitat use,
these two species exhibit different ways of
foraging. Pine voles store food in their
subterranean tunnels (Byers et al., 1976).
Meadow voles do not typically store food;
instead, they practice more of an "eat-as-you-go"
strategy.

Sociality is more strongly developed in pine
voles than in meadow voles. Pine voles live in
extended family units of two to nine animals,
typically consisting of two adult males, one
adult female, and one to two juveniles and
subadults (FitzGerald and Madison, 1983). Pine
voles appear to be monogamous, and recent
evidence suggests that only the dominant adult
female breeds in a family unit; reproductive
maturity of subadult females may be delayed by
as much as 83 days because of volatile chemical

FIGURE 1— Meadow vole, left. Photo by Maslowski. Pine vole, right. Photo by R. Patterson.

Reducing Wildlife Damage in Orchards

cues (pheromones) released by other family
members (Anonymous, 1985). The social system
of meadow voles is organized more loosely.
Meadow voles are promiscuous, and females are
territorial during the breeding season (Madison,
1980; Boonstra and Rodd, 1983). Extended
family groups do not occur except perhaps on a
limited seasonal basis.

Population reduction The most effective
and widely practiced method of controlling vole
damage relies on the use of toxic baits. Zinc
phosphide (ZP) is the least expensive and most
commonly used vole toxicant in Connecticut.
ZP is available in pellets or in grain bait
formulations and typically is hand-placed in the
runways or burrows of voles at a rate of
1-5 lbs/acre. To attract voles, prevent ingestion
by nontarget animals, and minimize exposure to
the elements, baits often are placed under a
protective cover (e.g., shingle, split tire).
ZP may also be broadcast in orchards at a rate
of 10-15 lbs/acre. ZP is a single-dose toxicant
capable of killing voles after one feeding.
Reductions in vole activity of 85-94% have been
associated with the use of ZP pellets; these
reductions were found primarily in studies
involving pine voles (Byers and Merson, 1982a,b;
Merson and Byers, 1985).

One problem with ZP is that ingestion of a
sublethal dose results in subsequent aversion to
the compound. Consequently, multiple-dose
toxicants that do not create a learned aversion
are sometimes used. Two such toxicants are
the anticoagulants chlorophacinone (Rozol) and
diphacinone (Ramik). Broadcast treatment of
chlorophacinone at 17-22 lbs/acre resulted in a
reduction in pine vole activity of 86-99%, and
similar treatments with diphacinone produced
62-81% control (Byers and Merson, 1982a; Merson
and Byers, 1985).

Because of their behavioral and ecological
differences, pine and meadow voles are affected
differently by toxic baits. Anticoagulant baits
are more effective against pine voles because
their habit of storing food promotes repeated
feeding on the bait by members of a family
group (Byers, 1984). In addition, hand placement
of toxic baits might be expected to control pine
voles better than meadow voles because the
majority of baiting is done within the dripline of
a row, whereas meadow voles are often found

outside this area and in adjoining habitats.

Snap trapping provides another means of
reducing vole populations. However, trapping is
probably impractical in large orchards because
many traps are required, the time necessary to
set and check traps is great, and "trap-shy"
individuals will not be captured.

Exclusion Tree guards may be useful in
reducing damage by meadow voles to young
trees, and expandable coil tree guards that are
wrapped around the main stem reduce
maintenance costs. These wraparound tree
guards generally are not effective against pine
voles, though, because of their burrowing habits
(Caslick and Decker, 1978). Hardware cloth
cylinders (1/4 inch mesh) buried to a depth of
6 inches have been suggested for exclusion of
pine and meadow voles from young trees
(O'Brien, 1983). If hardware cloth guards are
used, they should be fitted with 4-6 inch wide
aluminum flashing along the upper edge, because
our observations indicate that meadow voles can
easily climb hardware cloth. Also, the cylinders
should be spaced far enough from the tree to
permit trunk growth.

Cultural practices Cultural methods have
also reduced damage by voles. Minimizing the
amount of litter and vegetative cover under
trees reduces the desirability of the site to
voles. For instance, treatment of a 6-foot strip
centered on a tree row with the herbicides
simazine and glyphosate (4 and 1 lbs/acre) in
May followed with glyphosate in July (0.5%, spot
spray) reduced pine vole damage to Connecticut
apple trees by nearly 50% relative to unmowed
areas (Moore and Ahrens, unpubl. data). Control
of vegetation bordering orchards is also an
important consideration (Cummins et al, 1984),
especially when meadow voles are a problem.

Management of ground cover for vole control
has received some attention, but rigorous testing
has yet to be conducted. Traditionally, ground
covers in orchards are chosen for how well they
tolerate heavy equipment, conserve soil, and
retain nutrients and water. But ground cover
also serves as the food base for vole
populations, so ground covers should be chosen
with this in mind. One approach is to identify
plants that are unpalatable to voles and assess
their suitability as ground covers. For instance,
crown vetch (Coronilla varia), a legume, is

Connecticut Agricultural Experiment Station

Bulletin 855

unpalatable to voles and typically harbors low
densities of voles in natural settings (Jones 1978;
Lewis et al. 1983; and Byers 1984). In addition
to being unpalatable to voles, an established
field of crown vetch would not be invaded by
dandelions or other low-growing perennial forbs
(R. Peters, pers. commun.). However, crown
vetch is difficult to establish because of its
slow growth. Planting it in combination with
grass will aid in its establishment and prevent
invasion of other weeds. Once established,
crown vetch will outcompete grasses and should
be able to tolerate mowing two to three times
per growing season, but its ability to withstand
consistent traffic is unknown (N. Hartwig, pers.
commun.).

Horsfall et al. (1974), noting that voles
prefer forbs (e.g., clover, alfalfa) over grasses,
suggested that a reduction in damage to trees
would occur if the availability of alternative
foods such as broad-leaved forbs were increased.
Although short-term reductions in damage might
occur, it is likely that the increased survival
and reproduction of voles resulting from an
increased food supply could lead to serious
damage after 1-2 years of population growth,
particularly with the prolific meadow vole. A
more beneficial strategy, particularly in young
orchards without vole infestations, might be to
devise an herbicide program to encourage a
grass monoculture. For example, fall application
of 2,4-D reduces forbs and enhances turf growth
(J. Ahrens, pers. commun.). Fewer forbs could
aid control by reducing either the maximum
number of voles that the site could support, the
rate at which vole populations grow, or both.

Repellents We are testing compounds in
the laboratory for their ability to repel meadow
voles from apple stems. Thus far we have
examined three compounds: thiram, methiocarb,
and quebracho (a condensed tannin produced by
some plants). All exhibit significant degrees of
repellency. In preliminary studies, thiram
reduced damage by nearly 80% relative to
untreated controls. Methiocarb, which has been
used as a repellent of other wildlife species
(Conover 1982, 1985), reduced damage by about
68%. In Illinois, prairie voles, Microtus
ochrogaster, lost weight and averted from food
containing quebracho (Lindroth and Batzli, 1984).
In our experiments with meadow voles, two

mixtures of quebracho (1% and 3% of total dry
weight) reduced damage to stems by about 33%
and 68%, respectively.

Resistant trees Laboratory tests indicate
that voles prefer some varieties of apple trees
over others (Byers and Cummins, 1977;
Wysolmerski et al., 1980). A hybrid of Malus
prunifolia and M. sieboldii exhibits resistance to
damage by both pine and meadow voles,
primarily due to its taste and texture (Geyer
and Cummins, 1980). Resistance is transmitted
to an estimated 70% of the progeny
(J. Cummins, pers. commun.). The hybrid's
resistance to voles is not complete, though, for
Cummins et al. (1984) indicated that meadow
voles under hunger stress damaged it. The
rootstock, termed "Novole" and introduced by the
New York State Agricultural Experiment Station
as PI 286613, also is resistant to crown rot,
Phytophthora cactorum, and fire blight, Erwinia
amylovora (Cummins et al., 1983). It produces
vigorous standard trees, and hence should be
used as a trunk and root system with a high-
worked interstem of a dwarfing clone. PI286613
is patented but is not yet sold commercially.
No data exists on fruit production or quality.

Current work Common to virtually all the
control techniques discussed above is that their
effectiveness depends to varying degrees on vole
population sizes and food availability. For
instance, if vole numbers are low and alternative
foods are plentiful, a control technique may
appear to work well simply because conditions
mitigated against a severe problem. We are
conducting field experiments to enable us to
predict the effectiveness of a repellent as a
function of meadow vole density and the
availability of alternative food. These
experiments should allow us to predict the level
of protection afforded trees under a variety of
conditions, thereby enabling orchardists and
landowners to make better-informed decisions
when designing a strategy for vole control.

WHITE-TAILED DEER

Deer as agricultural pests In the early
1980s, Connecticut harbored an estimated 25,000
deer (Ellingwood and Spignesi, 1987). With this
growing population has come increasing problems
for apple growers and nurserymen because of

Reducing Wildlife Damage in Orchards

deer browsing. During the growing season, deer
consume some apple leaves, shoots, and ripening
fruit, but the damage usually is not extensive
enough to injure the plant. During the winter,
however, when food supplies are most limited,
damage to apple trees can become severe.
Katsma and Rusch (1980) found that removal of
40% of the buds on apple trees during the
winter led to a significant reduction in fruit
production the following year. Most vulnerable
are young apple trees. Deer browsing on the
leader branches may cause young trees to
become misshapen or stunted, thus lowering their
future fruit production (Harder, 1970).

Deer damage apple trees primarily by
browsing the terminal shoots of dormant twigs.
Browsed shoots 3-6 feet above the ground or
snow line are an indication of deer damage.
Deer browsing can be distinguished from rabbit
browsing by the ragged and torn appearance of
the ends of twigs. Twigs browsed by rabbits
are cut cleanly at an angle close to 45 . The
presence of deer can also be determined by
checking for tracks and oval-shaped fecal pellets.
Rabbits have more spherical, pill-shaped pellets.

Behavior and ecology Deer feed on a
variety of vegetation. In the summer, they
consume grass, forbs, and the leaves of many

SPINDLE TREE

JAPANESE YEW

ARBORVITAE

JAPANESE HOLLY

RED CEDAR

MOUNTAIN LAUREL
GOLDEN-BELLS
AMERICAN HOLLY
NORWAY SPRUCE
PEAR

50
% OF SHOOTS BROWSED

100

FIGURE 2 — Percent of shoots browsed by deer
on different plant species at the same location.

trees and shrubs. They also feed on farm crops
such as pumpkins, corn, and alfalfa. During the
winter when food supplies are low, deer survive
by utilizing fat reserves and by browsing on
buds and woody stems. Deer, however, do not
feed randomly; some plants such as yews and
apple trees are highly palatable, whereas other
plants such as scotch pine and pear are rarely
eaten by deer (Figure 2; Conover and Kania,
1988). Yet deer will browse small amounts of
almost any plant species. This is probably
advantageous as deer can consume small amounts
of many toxic plants without ill effects and a
varied diet helps insure that a deer will ingest
essential minerals and vitamins (Westoby, 1978).

White-tailed deer are normally sedentary,
restricting their activities to a home range of
less than a mile in diameter (Marchinton and
Hirth, 1984). Yet in any given year, some deer,
primarily young males, disperse by leaving their
home range to seek a new one. In one study
in Illinois, less than 10% of the adult deer
dispersed yearly, but 80% of the 1-year-old bucks
did so (Hawkins et al., 1971). Even for deer
that remain within their home range, however,
there are often seasonal shifts in the activity
center. These shifts usually occur as deer move
to take advantage of available food supplies
(Marchinton and Hirth, 1984). Both dispersal and
seasonal shifts in home range are important in
determining levels of damage in an orchard.
High rates of dispersal bring more deer in
contact with orchard trees, but for relatively
short periods of time. When deer adjust their
home ranges seasonally to include an orchard, a
longer tenure time is likely for each individual.
Thus, the relative contributions of transients and
residents to damage in an orchard may be
important in determining the effectiveness of
control methods such as repellents or population
reduction.

Males grow and shed antlers yearly. After
antler growth stops in late summer or early fall
bucks rub their antlers against trees, especially
saplings, to remove the protective covering
known as velvet. Bucks often rub trees hard
enough to remove the bark, break branches, or
knock the tree over. However, in the apple
orchards we examined in Connecticut, only a
few trees were lost this way yearly (Conover
and Kania, 1988).

Connecticut Agricultural Experiment Station

Bulletin 855

Population reduction Farmers who are
suffering from deer damage to their crops can
apply for crop damage deer permits, which allow
them or their agents to shoot deer on their
property from one half hour before sunrise to
one half hour after sunset throughout the year.
To obtain a permit, the farmer has to (1) earn
or have the potential to gross $500 per year
from his crops and (2) suffer confirmable deer
damage. Once an application is filed, the farm
will be inspected by the Department of
Environmental Protection for deer damage and to
insure that the site can be safely hunted. If
daytime hunting is ineffective because deer are
entering the property only after dark, farmers
can seek special permits to hunt at night.

Exclusion In many cases, erecting a deer-
proof fence may be the only available method
to stop deer from damaging a crop. The main
problem with fencing is the cost of construction,
but the cost can be amortized (Caslick and
Decker, 1977, 1979). There is much variation in
types of fences and their cost and effectiveness.
Temporary electric fences can be used to
discourage deer from entering a field (Porter,
1983). These fences work by altering a deer's
behavior rather than by physically preventing it
from crossing. They are most effective when
farmers can anticipate a problem with deer and
turn the electricity on before damage begins.
These fences are inexpensive; cost, excluding
labor, is about $0.10 per foot (Craven and
Hygnstrom, 1987). With an electric fence, it is
probably worthwhile to pay extra for a powerful
electric charger, because the fence has to
provide enough of a jolt to discourage the deer
from trying to go through the fence again.

Permanent electric fences are usually made
of high-tensile fencing; cost, excluding labor,
ranges from $0.50-$1.50 per foot (Palmer et al.,
1985; Craven and Hygnstrom, 1987). Two types
are commonly used. One is a vertical six-wire
fence with the bottom wire 8 inches above the
ground and the other wires spaced one foot
apart. The other type is a slant design where
the fence is installed at a 45 angle facing
outward. Both designs have worked well in
excluding deer (Palmer et al., 1985; Ellingwood
et al., 1985).

Permanent woven wire fences are very
effective in keeping deer out of fields but are

difficult to construct and cost $2-4.00 per foot,
excluding labor (Craven and Hygnstrom, 1987).

Cultural practices When establishing a new
orchard, farmers should consider whether deer
are likely to pose a major problem. To
examine whether deer damage is likely to occur
at any particular site, we compared extent of
damage to yews in nurseries to several
characteristics of the nursery itself. For each
nursery examined, we recorded: (1) its size and
proximity to houses and roads; (2) the size of
woodlots both adjoining and not adjoining but
less than 2 km from the nursery; (3) the size
and density of the local deer population; and
(4) the amount of alternate food available to
deer. We found that, of these characteristics,
deer damage was best correlated with the
number of deer in the adjoining woodlots.
Hence, farmers can assess the potential for deer
damage at a site, even before it is planted, by
estimating the number of deer in adjacent
woodlots. The latter is relatively easy to
measure by counting the number of deer pellet
groups in several randomly-selected plots in the
adjacent woodlots. A formula can then be used
to convert this data to deer numbers (Neff,
1968). If damage is likely at a site, some
preventative steps can be taken to reduce the
potential problem. For instance, it may be
worthwhile to erect a deer-proof fence at the
outset.

More damage will occur in a small orchard
than in a large one because a larger percentage
of trees will be close to the edges of woods.
Hence, deer damage may be less if all apple
trees are located in one large field rather than
scattered in several small fields. Deer damage
will be reduced if apple orchards are placed
away from woodlots. Dwarf and semidwarf
trees are more vulnerable to damage than
standard trees because more of their foliage is
within reach of deer. Peaches, pears, and
blueberries, which are less palatable to deer
than apples, may be better crops in isolated
fields where damage is expected.

Planting of diversionary crops has been
suggested as a means of reducing deer damage.
The idea is that deer will feed on diversionary
crops and leave apple trees alone. Two
problems limit the usefulness of this method.
First, the deer population will increase because

Reducing Wildlife Damage in Orchards

more will survive the winter and their breeding
success will increase because they will be in
better condition. In one study, when
supplemental food was provided for 5 years to
deer in a 622-acre enclosure, the herd increased
from 23 to 159 (Ozoga and Verme, 1982).

The second problem is that by providing a
palatable food for deer, especially during winter,
a farmer may attract a higher percentage of
the local deer to his orchard (Matschke et al.,
1984). This problem is compounded by the fact
that deer often browse on available plants as
they pass by them. Hence, while deer may fill
most of their nutritional needs on the
diversionary crop, they may still browse on the
apple trees. This suggests that a diversionary
crop may be most useful if planted away from
the apple orchard but within the home range of
the deer browsing in the apple orchard. The
winter of 1986-1987, we conducted a preliminary
experiment to try to divert deer from nursery
plants by providing diversionary food
approximately 200 yards away when several
inches of snow covered the ground. The
ittempt apparently failed, however, as deer
damage to the nursery plants was similar to
what it had been the year before. Changes in
the number of deer or their movements could
have influenced our results; thus, this experiment
is being continued over the next few years.

One problem we face is that we do not
know the optimal distance to locate a
diversionary crop from a nursery or orchard.
Therefore, we are examining the home range of
deer by placing radio transmitters on animals
caught in and adjacent to nurseries. By
tracking their movements during the course of a
year, we will collect information on the size of
areas used by individuals, seasonal shifts in areas
used, and the timing of use of agricultural
areas. By assessing movements of deer in and
around nurseries, this study may also prove
useful in determining how successful removal
programs are.

Repellents Several chemicals are sold as
deer repellents, and home-made remedies abound.
Unfortunately, little information is available
about their effectiveness. We tested six
repellents in commercial nurseries in Connecticut
to determine if they could reduce deer damage
to Japanese yews, Taxus cuspidata, (Conover,

1984, 1987). In this experiment, 0.025 acre plots
were established within large fields of yews.
Some plots were treated with one of the
repellents while others were left untreated as a
control. The amount of deer browsing in these
plots was monitored throughout the winter. By
winter's end, deer browsing was 15% to 46%
lower in the treated plots than in the untreated
control plots (Figure 3). We further tested the
two most effective repellents, BGR and Hinder,
by spraying 0.5 acre plots of yews with them
(Conover, 1987). In this test, deer browsing was
reduced by about 50% by winter's end in both
BGR and Hinder plots compared to the untreated
control plots.

We also tested the effectiveness of BGR,
human hair, and a mixture of blood meal and
peppercorns in reducing deer damage to young
apple trees. In one orchard, deer browsed an
average of 1.1 buds per untreated tree, 0.8 on
trees treated with BGR, and 0.5 on trees
treated with human hair. In another orchard,
deer browsed an average of 2.9 buds on
untreated trees, 1.1 on trees with bags containing
human hair and 1.2 on trees with bags
containing blood meal and peppercorns. Thus, in
all of these tests repellents reduced damage by

OCT

JAN

APR

FIGURE 3— Percent reduction in browsing in
plots of yews treated once in the fall with a
repellent when compared to nearby plots left
untreated.

10

Connecticut Agricultural Experiment Station

Bulletin 855

25-50%, but no repellent eliminated damage
entirely.

Cost is an important consideration in
selecting a repellent. Materials to make bags
containing human hair or blood meal and
peppercorns are inexpensive but considerable
labor is required to make the bags and tie them
to the trees. In contrast, some spray repellents,
such as BGR, are costly to purchase but require
less labor to use.

WOODCHUCKS

Woodchucks as agricultural pests The
woodchuck is a ground-dwelling member of the
squirrel family which commonly inhabits orchards
in Connecticut. Three of their activities may
present problems for orchardists: burrows and
associated mounds of excavated soil can be
hazardous to machinery; burrows at the base of
trees may cause excessive aeration of roots and
upheaval of the tree; and gnawing and clawing
of fruit trees can severely damage or even kill
young trees. Gnawing damage usually occurs on
the main stem of trees located close to burrows
and can be distinguished from vole gnawing by
the larger size of the incisor marks (1/8 to
3/8 inch wide). Woodchucks also climb trees

fk\

r

%

a

FIGURE 4— Although primarily found on or under
the ground, woodchucks will climb trees, often
using them as sunning posts. This woodchuck is
eight feet above the ground in a peach tree.
Photo by P. Picone.

(Figure 4; Swihart, 1982) and damage lower
branches. Clawing of trees results in shredded
bark 1 to 3 feet above the ground.

Behavior and ecology Woodchucks are true
hibernators, usually becoming inactive in
November and emerging from burrows in March.
Hence, unlike voles and deer, woodchucks do not
cause damage during the winter. Breeding
occurs in early spring, and an average of four
young are born after a 32-day gestation period.
Woodchucks are primarily active around dawn
and dusk, with little above ground movement
occurring from 10:30 p.m. to 6:00 a.m.
(Merriam, 1963).

Population reduction Orchardists typically
rely on lethal control techniques. Poisonous gas
introduced into sealed burrows is one method
used (Byers, 1984). By monitoring burrows
treated by a landowner, we found that 10 of 35
burrows (28%) had been reoccupied within 2 days,
83% within 2 weeks, and 86% within 1 month of
treatment. Part of the reason for the short-
term effectiveness of the treatment in this case
may have been due to its timing. Treatment of
burrows occurred during the day when
woodchucks were least likely to occupy their
burrows. Although we have no data on the
proportion of burrows occupied by residents
which survived the treatment, it is likely that
survivors reopened the burrows on the same day.
In addition, our findings indicate that several
woodchucks may use a single burrow, albeit
usually not at the same time. This also would
contribute to a rapid reoccupation of empty
burrows.

The removal of woodchucks by shooting or
trapping also has not been demonstrated to be
effective in protecting an orchard. During a
4-year population study in Pennsylvania, a total
of 1040 woodchucks were removed from a 600-
acre site by shooting or trapping (Davis et al.,
1964). Nonetheless, the population size at this
site was unaffected, primarily because of
increased juvenile survival, higher birth rates,
and substantial immigration (Davis et al., 1964).

Exclusion Woodchucks may be excluded
from small areas by combining a 4- foot high
hardware cloth fence buried 10-12 inches with
an electric hot-shot wire 4-5 inches high outside
the fence (Bollengier, 1983). Exclusion usually is
not practical for commercial growers.

Reducing Wildlife Damage in Orchards

11

Current work We have initiated a field
study of woodchucks with the intent of learning
more about their social system, behavior, and
ecology. By mapping burrow systems, monitoring
the movements of radio-collared individuals, live-
trapping animals, and measuring various features
of the habitat around burrows, we are examining
aspects of woodchuck movements, habitat use,
burrow placement, and population ecology that
should prove useful in devising effective controls.

We are investigating two ways of reducing
damage caused by woodchuck gnawing and
clawing. First, we are examining ways of
increasing the amount of time before an empty
burrow is recolonized by a woodchuck. Wild
canids such as foxes and coyotes are natural
predators of woodchucks which also modify
woodchuck burrows into dens for their own use
(Grizzell, 1955; Parker, 1986). We are testing
predator odors for their ability to repel
woodchucks from a burrow by spraying the
entrance area with fox or coyote urine and
noting how long it takes for recolonization to
occur relative to untreated control burrows.
Odors of naturally-occurring predators have been
used successfully to modify feeding behavior of
snowshoe hares (Sullivan, 1986; Sullivan and
Crump, 1984, 1986).

A second experiment involves the use of
"gnawing" posts to protect young fruit trees.
Woodchucks presumably gnaw trees to wear down
their incisors and/or to communicate with other
woodchucks by leaving their scent on the tree.
By providing alternative sites adjacent to trees,
it may be possible to shift most of the gnawing
activity from the trees to the posts.

SUMMARY

The most common method of controlling
voles in orchards is use of the toxicants zinc
phosphide, chlorophacinone, or diphacinone.
Herbicide treatments to reduce growth of
herbaceous plants in orchards also have been
effective against voles. Deer damage can be
reduced by installing fences, applying repellents,
or using cultural techniques. Removing pest
deer by hunting is another option. Woodchucks
are controlled in a variety of ways aimed at
population reduction. Unfortunately, these
methods are not always effective.

When choosing a control strategy, an
understanding of the behavior and ecology of the
pest species is helpful. Past techniques which
have ignored these facets of a species' biology
often have failed. In addition, an understanding
of the pest population as a dynamic, constantly
changing group of individuals is important. For
instance, dispersing animals may quickly settle
into an area following a population decline.
Because of this, removal techniques usually offer
only short-term solutions. Modifying the
animal's behavior and devising ecologically sound
control measures offer considerable promise for
longer-term solutions to pest problems in
orchards.

LITERATURE CITED

Anonymous. 1985. Coming of age. Research
Perspectives, North Carolina Agric. Res. Serv.,
4(3):9.

Anthony, R.G. and A.R. Fisher. 1977. Wildlife
damage in orchards — a need for better
management. Wildl. Soc. Bull. 5:107-112.

Batzli, G.O. 1985. Nutrition. Pages 779-811
in R.H. Tamarin (ed.) Biology of New World
Microtus. Special Publ. No. 8, Amer. Soc.
Mammal.

Bee, J.W., G.E. Glass, R.S. Hoffmann and
R.R. Patterson. 1981. Mammals in Kansas.
Publ. Educ. Series No. 7, Museum of Natural
History, Univ. of Kansas, Lawrence. 300 pp.

Bollengier, R.M., Jr. 1983. Woodchucks. Pages
B-153 to B-156 in R.M. Timm (ed.), Prevention
and control of wildlife damage. Great Plains
Agric. Council Wildl. Resour. Comm. and Coop.
Ext. Serv., Inst, of Agric. and Nat. Resour.,
Univ. Nebraska, Lincoln.

Boonstra, R. and F.H. Rodd. 1983. Regulation
of breeding density in Microtus pennsylvanicus.
J. Anim. Ecol. 52:757-780.

Byers, R.E. 1984. Control and management of
vertebrate pests in deciduous orchards of the
eastern United States. Hort. Rev. 6:253-285.

Byers, R.E. and J.N. Cummins. 1977.
Variations in susceptibility of apple stems to

12

Connecticut Agricultural Experiment Station

Bulletin 855

attack by pine voles. J. Amer. Soc. Hort. Sci.
102:201-203.

Byers, R.E. and M.H. Merson. 1982. Current
improvements in baiting pine and meadow voles.
Pages 139-142 in R.E. Marsh (ed.) Proc. 10th
Vert. Pest Conf.

Byers, R.E., R.S. Young and R.D. Neely. 1976.
Review of cultural and other control methods
for reducing pine vole populations in apple
orchards. Pages 242-253 in C.C. Siebe (ed.)
Proc. 7th Vert. Pest Control Conf.

Caslick, J.W. and D.J. Decker. 1977. Benefit-
cost analysis of a deer-proof fence for apple
orchards. Conserv. Circ. 15(4), Dept. Nat.
Resour. N.Y.S. Coll. of Agric. & Life Sci.,
Cornell Univ., Ithaca. 3 pp.

Caslick, J.W. and D.J. Decker. 1978. Control
of wildlife damage in orchards and vineyards.
Cornell Univ. Coop. Ext. Info. Bull. 146:1-18.

Caslick, J.W. and D.J. Decker. 1979. Economic
feasibility of a deer-proof fence for apple
orchards. Wildl. Soc. Bull. 7:173-175.

Conover, M.R. 1982. Behavioral techniques to
reduce bird damage to blueberries: methiocarb
and a hawk-kite predator model. Wildl. Soc.
Bull. 10:211-216.

Conover, M.R. 1984. Effectiveness of repellents
in reducing deer damage in nurseries. Wildl.
Soc. Bull. 12:399-404.

Conover, M.R. 1985. Using conditioned food
aversions to protect blueberries from birds:
comparison of two carbamate repellents. Appl.
Anim. Behav. Sci. 13:383-386.

Conover, M.R. 1987. Comparison of two
repellents for reducing deer damage to Japanese
yews during winter. Wildl. Soc. Bull. 15:265-268.

Conover, M.R. and G.S. Kania. 1987.
Effectiveness of human hair, BGR, and a
mixture of blood meal and peppercorns in
reducing deer damage to young apple trees.
Proc. East. Wildl. Damage Control Conf. (In
press).

Conover, M.R. and G.S. Kania 1988. Browsing
preference of white-tailed deer for different
ornamental species. Wildl. Soc. Bull. (In press).

Cranford, J.A. and T.L. Derting. 1983. Intra
and interspecific behavior of Microtus
pennsylvanicus and Microtias pinetorum. Behav.
Ecol. Sociobiol. 13:7-11.

Craven, S. and S. Hygnstrom. 1987. Controlling
deer damage in Wisconsin. Univ. Wise, Coop.
Ext. Serv. Bull. G3083, 12pp.

Cummins, J.N., H.S. Aldwinckle and R.E. Byers.
1984. 'Novole': a crabapple selected for
resistance to pine voles and meadow voles.
HortScience 19:162.

Cummins, J.N., H.S. Aldwinckle and R.E. Byers.
1983. 'Novole' apple. HortScience 18:772-774.

Davis, D.E., J.J. Christian and F. Bronson.
1964. Effect of exploitation on birth, mortality,
and movement rates in a woodchuck population.
J. Wildl. Manage. 28:1-9.

Ellingwood, M. and J. Spignesi. 1987.
Connecticut deer program summary 1980-1984.
Conn. Dept. Envir. Prot., Wildl. Bureau Publ.
DR-7, 16pp.

Ellingwood, M.R., J.B. McAninch and M.J.
Fargione. 1985. Current status of deer fencing in
the Northeast. Pages 180-185 in P.T. Bromley
(ed.), Proc. 2nd East. Wildl. Control Conf.

Ferguson, W.L. 1980. Rodenticide use in apple
orchards. Pages 2-8 in R.E. Byers (ed.), Proc.
4th Eastern Pine and Meadow Vole Symp.

FitzGerald, R.W. and D.M. Madison. 1983.
Social organization of a free-ranging population
of pine voles, Microtus pinetorum. Behav. Ecol.
Sociobiol. 13:183-187.

Getz, L.L. 1985. Habitats. Pages 286-309 in
R.H. Tamarin (ed.) Biology of New World
Microtus. Special Publ. No. 8, Amer. Soc.
Mammal.

Geyer, L.A. and J.N. Cummins. 1980. Textural
and taste influences on gnawing by pine voles.
Pages 43-49 in R.E. Byers (ed.), Proc. 4th
Eastern Pine and Meadow Vole Symp.

Grizzell, R.A., Jr. 1955. A study of the
southern woodchuck Marmota monax monax.
Amer. Midland Natur. 53:257-293.

Reducing Wildlife Damage in Orchards

13

Harder, J.D. 1970. Evaluating winter deer use
of orchards in western Colorado. Trans. N. Am.
Wildl. Conf. 35:35-47.

Hawkins, R.E., W.D. Klimstra, and D.C. Autry.
1971. Dispersal of deer from Crab Orchard
National Wildlife Refuge. J. Wildl. Manage.
35:216-220.

Horsfall, F., Jr., R.E. Webb and R.E. Byers.

1974. Dual role of forbs and rodenticides in

the ground spray control of pine voles. Pages

112-125 in Proc. 6th Vert. Pest Control Conf.

Jones, E.N. 1978. Influences of crownvetch
(Coronilla varia L.) on the density and spatial
distribution of the meadow vole (Microtus
pennsylvanicus). Unpubl. M.S. Thesis,
Pennsylvania State University. 52 pp.

Katsma, D.E. and D.H. Rusch 1980. Effects of
simulated deer browsing on branches of apple
trees. J. Wildl. Manage. 44:603-612.

Keller, B.L. 1985. Reproductive patterns.
Pages 725-778 in R.H. Tamarin (ed.) Biology of
New World Microtus. Special Publ. No. 8, Amer.
Soc. Mammal.

Lewis, E., D.H. Rhodes and M. Richmond. 1983.
Acceptability of six candidate groundcovers to
meadow voles. Pages 87-92 in R.E. Byers (ed.)
Proc. 7th Eastern Pine and Meadow Vole Symp.

Lindroth, R.L. and G.O. Batzli. 1984. Plant
phenolics as chemical defenses: effects of
natural phenolics on survival and growth of
prairie voles (Microtus ochrogaster). J. Chem.
Ecol. 10:229-244.

Madison, D.M. 1980. Space use and social
structure in meadow voles, Microtus
pennsylvanicus. Behav. Ecol. Sociobiol. 7:65-71.

Marchinton, R.L. and D.H. Hirth. 1984.
Behavior. Pages 129-168 in L.K. Halls (ed.)
White-tailed Deer Ecology and Management.
Stackpole Books, Harrisburg, PA.

Matschke, G.H., D.S. deCalesta, and J.D. Harder.
1984. Crop damage and control. Pages 647-654
in L.K. Halls (ed.) White-tailed Deer Ecology and
Management. Stackpole Books, Harrisburg, PA.

Merriam, H.G. 1963. Low frequency telemetric
monitoring of woodchuck movements. Pages

155-171 in L. Slater (ed.) Bio-telemetry.
Pergamon Press, New York.

Merrill, H.A. 1939. Rodent control. Conn.
Agric. Exp. Stn. Bull. No. 434, pp. 254-258.

Merson, M.H. and R.E. Byers. 1985.
Weathering and the field efficacy of pelletized
rodenticide baits in orchards. Crop Protection
4:511-519.

Miller, D.H. and L.L. Getz. 1969. Life-history
notes on Microtus pinetorum in central
Connecticut. J. Mammal. 50:777-784.

Neff, D.J. 1968. The pellet-group count
technique for big game trends, census, and
distribution: a review. J. Wild. Manage. 32:597-
614.

O'Brien, J.M. 1983. Voles. Pages B-147 to B-
152 in R.M. Timm (ed.) Prevention and Control
of Wildlife Damage. Great Plains Agric. Council
Wildl. Resour. Comm. and Coop. Ext. Serv., Inst,
of Agric. and Natur. Resour., Univ. Nebraska,
Lincoln.

Ozoga, J.J. and L.J. Verme. 1982. Physical
and reproductive characteristics of a
supple men tally-fed white-tailed deer herd. J.
Wildl. Manage. 46:281-301.

Palmer, W.L., J.M. Payne, R.G. Wingard, and
J.L. George. 1985. A practical fence to reduce
deer damage. Wildl. Soc. Bull. 13:240-245.

Parker, G.R. 1986. The seasonal diet of
coyotes, Cam's latrans, in northern New
Brunswick. Canadian Field-Naturalist 100:74-77.

Porter, W.F. 1983. A baited electric fence for
controlling deer damage to orchard seedlings.
Wildl. Soc. BuU. 11:325-327.

Richmond, M.E., C.G. Forshey and P.N. Miller.
1988. An experimental analysis of effects of
known pine vole populations on tree root
girdling, tree vigor, and fruit production. Proc.
3rd Eastern Wildl. Damage Control Conf., in
press.

Schadler, M.H. and G.M. Butterstein. 1979.
Reproduction in the pine vole, Microtus
pinetorum. J. Mammal. 60:841-844.

14

Connecticut Agricultural Experiment Station

Bulletin 855

Sullivan, T.P. 1986. Influence of wolverine
(Gulo gulo) odor on feeding behavior of snowshoe
hares (Lepus americanus). J. Mammal. 67:385-
388.

Sullivan, T.P. and D.R. Crump. 1986. Feeding
responses of snowshoe hares (Lepus americanus)
to volatile constituents of red fox (Vulpes
vulpes) urine. J. Chem. Ecol. 12:729-739.

Sullivan, T.P. and D.R. Crump. 1984.
Influences of mustelid scent-gland compounds on
suppression of feeding by snowshoe hares (Lepus
americanus). J. Chem. Ecol. 10:1809-1821.

Sullivan, W.T., Jr., T.B. Sutton and D.W. Hayne.
1980. Apple tree mortality, rate and causes.
Pages 62-65 in R.E. Byers (ed.) Proc. 4th
Eastern Pine and Meadow Vole Symp.

Swihart, R.K. 1982. Scansorial behavior in
woodchucks, Marmota monax. Canadian Field-
Nat. 96:215-216.

Swihart, R.K., N.A. Slade, and B.J. Bergstrom.
1988. Relating body size to the rate of home-
range use in mammals. Ecology, in press.

Westoby, M. 1978. What are the biological
bases of varied diets? Amer. Nat. 112:627-631.

Wysolmerski, J.C., R.E. Byers and J.N. Cummins.
1980. Laboratory evaluation of some Malus
clones for susceptibility to girdling by pine
voles. J. Amer. Soc. Hort. Sci. 105:675-677.

I The Connecticut Agricultural Experiment Station ,

founded in 1875, is the first experiment station in America. It is chartered
by the General Assembly to make scientific inquiries and experiments
regarding plants and their pests, insects, soil and water, and to perform analyses for State
agencies. The laboratories of the Station are in New Haven and Windsor; its Lockwood
Farm is in Hamden. Single copies of bulletins are available free upon request to Pub-
lications; Box 1 106; New Haven, Connecticut 06504. ISSN 0097-0905

University of
Connecticut

39153028932061

^

3

BE

• ■ '■
1 V-

'' 9

>', •>

= ••■, ■,■■...■.■■■-.■■.= • ■•'■>•;. ■'■ -v.' '' '' •

■■■■> .<■'■'*■•' '■.

■ ' 9 •'■■■' ■ ••' iH ' L': Hit ' ' * ' '■;■*' H

' H ^a" V-'V.'a \-K-^-^— va-

. ■■ ■ "'A: ■,:,.'£'• ' ;•■--"''' '■■'■ A\'A '■*•' A •. A-— " A

.;■<-.. a AAA. ;■■ ,a a a,. ■•,,,; •••;'.*:;•,

',*■■■?>, or-:.. ' -.

■

'■'•-'''.'"■ I ".■•'•.:■■>'"''•-' £f ■ "■ • '*..■'■'■••

■H •■ ■■" IKdHi '.! '. ■■■.......-'..■ j- • :->.

■ MS UHK WSaHSm& S RM ■" ?:,.y';'-..<, A "

$$$§il PS^IiBI ": ;-' a a.a

I'.-vl1^;.' • ■./'"■'•

r-;-e.AAAcA-,,,-A^' :

wm

mm

%&ffl@B®8m

obu ingui uiea /{3feVs.itf'4t 8*8**1™ ..^ckWE-v'*

ii»

HHs^lBHiBl

■■'■■■■ ' VJ" ;■'■■;:■'■ ,'V.-'. ■•- . V- rv '■'.'.:■...';..•-':.,-,: • ■
•■•■■•■

lllliiiii&l

^•X^^^^rJ^^.I^^Ki

Sift