Vertebrate Pest Management
Excerpt from Publication 310, Integrated Pest Management
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Table of Contents
- Description, Biology, Damage
There are several vertebrate pests that cause economic damage in apple orchards. These include a number of mammal species including voles (often referred to as field mice), woodchucks (ground hogs), rabbits, deer and several species of birds (crows, starlings, grackles).
No single method of vertebrate pest management is completely effective. A season-long management strategy - including cultural, mechanical and biological methods and deterrents - is often the most effective way of minimizing economic losses from these animals.
Description, Biology, Damage
Table 4-18. Common vertebrate pests of apple orchards.
Meadow vole (field mouse) Microtus pennsylvanicus Body 90-130 mm long, dark chestnut brown with grayish belly. Ears smaller and tail shorter (35-65 mm) than that of mice. Feeds on grasses, sedges, seeds, grains and tree bark. Makes surface runways in grass. Active day and night. Litters of 3-7 are produced throughout year. Population levels fluctuate widely, with a 3-4 year cycle. Grasslands, meadows, fence rows, with plenty vegetation and orchard sods. Primarily live above ground in dense sod or vegetation. Common throughout Ontario. Feeding injury and girdling of bark of apple trees, particularly in winter when cover is present. May result in tree stress or death. Pine vole, Pitymys pinetorum Body 70-110 mm long, auburn brown fur, very thick and soft. Tail shorter than meadow voles at 17-25 mm. Feeds on tubers, bulbs, seeds and root bark. Tunnels through leaf mold and loose topsoil layers near surface. Nests beneath logs stumps and other cover. Most often found in eastern deciduous woods, occasionally in orchards. Live primarily below the ground and damage the root systems of trees. Present south of line between Goderich and Ottawa. May tunnel around orchard trees and feed on bark of roots and young, feeder roots. Results in tree stunting or, sometimes, death if feeding is extensive. Damage to apple orchards has only been observed rarely in southwestern Ontario. Woodchuck (Groundhog) Marmota monax Body 40-45 cm long, heavy-bodied, yellowish brown to brown, pale brown belly. Feet dark brown or black, tail 10-18 cm. Weight ranges from 2.2-4.5 kg. Generally diurnal, feeding on a wide range of young, succulent plants. Dens in underground burrows with two or more openings. Breeds once a year with 2-6 young born in April or May. Hibernate during winter. Open woods, ravines, regeneration areas, orchards. Common throughout Ontario. Damage ranges from bark injury (gnawing) to root damage caused by burrowing. These burrows may also be a hazard to equipment and people inadvertently stepping into the hole, resulting in possible physical injury. Eastern Cottontail Sylvilagus floridanus Body 35-45 cm long with rather short ears (65-75 mm) for a rabbit. Colour brown to grey with white cottony tail. Feet whitish. Weight ranges 1.0-1.8 kg. Feeds on green vegetation in summer, bark and twigs in winter. Nocturnal with activity from early dusk to late morning. Dens in brush piles, high vegetation or in shallow underground burrows, 3-4 litters per year, each with 4-7 young born. Populations are cyclical. Open woods, heavy brush, regeneration areas. Common throughout southern Ontario below line from Parry Sound to Ottawa. During winter feed low on tender terminal growth and fruit buds, resulting in "witches broom" growth. Girdling of bark results in loss of tree vigour or death. European Hare (jackrabbit) Lepus europaeus Body 63-70 cm long with long ears (11-13 cm). Brownish grey colour, tip of tail black. Weigh up to 4 kg. Feeds on green vegetation in summer, twigs and bark in winter. Active from early dusk until morning. Several broods per year. Open fields and low hills. Confined to southern Ontario below Algonquin Park. Most common in southwestern and southcentral Ontario. Similar to Eastern cottontail but damage to upper limbs (within 1 m of ground) more severe due animal's ability to stand on hind legs to get hard to reach limbs. White-tailed Deer Odocoileus virginanus Height 90-110 cm. Largest North American deer with females up to 110 kg and males up to 180 kg. Fur blue-grey to brown. Males have antlers. Long white tail is characteristic. Browses on twigs, shrubs, herbaceous plants, acorns and grasses. Active mainly at dusk until dawn, 1-2 young per year. Congregate in "wintering grounds" that may include orchards. Deciduous woods, open brush, regeneration areas, second-growth forests. Common throughout Ontario, south of Timmins. In winter and early spring, feed on soft tender tips and terminal growth. This "nipping" results in loss of fruit buds, and more importantly, tree shape. Smaller trees may also be damaged by rubbing of antlers to remove "velvet," polish or serve as communication posts. This injury occurs in the fall (September to mid November). Crows, starlings, grackles, other black birds Various Starlings, grackles and other black birds often flock together and pass through orchards near or at harvest. Crows are more solitary or in small groups. Adapted to wide range of habitats. Crows often nest in conifers, such as pine plantations. Common throughout Ontario. Birds occasionally peck apples. This injury is most often seen on well-exposed fruit at the tops of trees.
Managing vertebrate pests is only used if economic injury has occurred or is imminent.
A variety of natural predators such as hawks, owls, crows, ravens, weasels, foxes, coyotes, raccoons, skunks, cats and snakes feed on voles. Predation may not manage high vole populations, but helps manage populations in normal years to prevent some damage.
Cultural practices reduce or even eliminate the need for toxic baits. Voles require green, growing vegetation for survival (protection from predators, access to food) and breeding. Reducing or eliminating long grass and cover through mowing and herbicide treatment lowers rodent numbers. Mow grass to 8-15 cm. Avoid waiting long intervals between mowing, or using a sickle-bar mower since it may produce a thatch layer that provides cover for voles. Avoid leaving mulch, prunings, windfall fruit or decaying vegetation around the base of trees or in tree rows. These practices provide outstanding meadow vole control but do not eliminate pine voles.
Toxic baits provide reliable control in orchards where voles are abundant. Avoid using poison-coated corn baits or broadcasting poison baits on the orchard floor - they are poisonous to farm pets, wild turkeys, pheasants, raccoons, skunks and other non-target wildlife. Bait stations provide long-term management of voles, and have less impact on non-target organisms. Slabs of wood, pieces of board or tin cans, with one end removed, are used for bait stations. Bait is placed under the board or in the can with the can lying on its side. The inverted T bait station is made of 1½ -inch ABS pipe and is probably the most effective type of bait station available. In this station, place several tablespoons of bait in the neck, which is capped protecting the bait from the elements, and use 25 stations per ha (10 per acre). Bait stations are most effective if dropped apples are picked up and removed from the orchard before first snowfall. Common rodenticides used as bait are zinc phosphide-treated baits, dipacinon (Ramik Brown) and chlorophacinone (Rozol, Groundforce).
Place mouse guards around trees to prevent voles from damaging the bark. Use guards on young trees where small amounts of vole damage can severely damage or kill the tree. Be sure guards are approximately 45 cm high and buried 5 cm deep in the soil. Check mouse guards each year to make sure they are working and ensure that they are not interfering with trunk expansion. Avoid the use of guards which do not allow air circulation. Always use light coloured tree guards since dark materials increase the temperature of the bark on sunny days in winter and low temperatures at night cause injury to bark tissue.
Cats, dogs, foxes, owls and hawks are all excellent predators of rabbits and hares. Plant orchards away from natural meadows or brush to reduce pest pressure. Eliminate brush piles, weed patches, junk dumps and stone piles in or adjacent to the orchard, where rabbits can live and hide. Paint trunks and lower scaffolds with white exterior latex paint and thiram to repel rabbits. Hunting is also an effective method of control. Live traps control small rabbit populations, but are less effective on large populations because time and labour costs are prohibitive. Purchase traps at hardware, agricultural supply and feed stores or sporting good stores. Bait traps with corn, oats or apples during the fall and winter. Within 24 hours of the live capture of a nuisance animal:
- release it in close proximity to where it was caught (up to
a maximum of one kilometre) as directed by Ministry of Natural
- if it is sick, injured or immature, turn it over to a veterinarian
or an authorized wildlife custodian, or
- humanely euthanize it
Predators of woodchucks include hawks, owls, foxes coyotes, weasels, dogs and humans. Many woodchucks are killed on roads by automobiles. There are several commonly used methods to control woodchucks.
Phostoxin - a fumigant containing aluminum phosphide. In the presence of moisture in the burrow, phostoxin produces hydrogen phosphide (phosphine) gas that is effective against groundhogs. Soil moisture and a tightly sealed burrow system are important when using this product. Wear a full-face mask respirator with an acid gas canister when handling phostoxin, cotton gloves are also recommended. Have a second person wearing personal protective equipment to assist during fumigation. Always consult the product label. To avoid unintentional poisonings of endangered, threatened or vulnerable species, confirm that the burrow, den or tunnel is inhabited by the pest before applying this product. This product is only to be used by individuals trained in the application of aluminum phosphide who either hold, or are supervised by persons who hold, a pesticide applicator certificate or license recognized by the provincial/territorial pesticide regulatory agency where the application occurs.
Gas cartridges (carbon monoxide) - one of the most common methods of woodchuck control. These cardboard cylinders contain a mixture that burns slowly and asphyxiates the groundhog. The cartridge is ignited and placed in the burrow of the groundhog and all entrances are sealed. As the cartridges burn, they produce carbon monoxide and other gases lethal to woodchucks. This method is most effective in the spring before young emerge, but burrows can be treated with gas cartridges at any time. Follow manufacturer's instruction on the preparation and use of cartridges.
Trapping - can be effective for groundhog control, but is time consuming. Place a live trap at the burrow entrance, in major travel lanes or at the site of damage. Place guide logs on either side to help funnel the animal into it. Cover the trap with dark canvas or grass to hide it. Bait traps with apple slices, carrots, cantaloupe pieces, lettuce, cabbage or fresh peas. Replace the bait daily and remove the spoiled baits. Check traps at least twice a day and clean after each catch. Within 24 hours of trapping the animal, release it in close proximity to where it was caught (up to a maximum of one kilometre) in a suitable habitat as directed by MNR. If it is sick, injured or immature, turn it over to a veterinarian or an authorized wildlife custodian or humanely euthanize it. Avoid trapping and relocating woodchucks in the autumn right before hibernation or during the spring while the young are in the dens. Animals trapped and released before hibernation may not be able to find a winter den. Relocating female woodchucks in the spring may kill their young.
Shooting - is another control measure for woodchucks. They can be shot anytime of the year if they are damaging property. If done properly, shooting reduces woodchuck populations or maintain low populations of woodchucks.
There are several different types of fences available - including woven wire fence - which are excellent options for areas where deer densities are high and the likelihood of damage is great. Permanent woven wire fence provides a barrier that requires little maintenance but can be expensive to install. The costs of these fences often limit their use around orchards, with the exception of nurseries. The 2.44 m high, vertical fence is constructed from two 1.22 m sections of 15.24 cm x 30.50 cm wire mesh, joined with hog rings. Two or more strands of barbed wire spaced 25 cm apart are added to the top of the structure extending the overall height to 3.05 m or more. Research in New York indicates that when feeding pressure is high, blocks larger than 20.23 ha usually require this type of fencing to reliably prevent deer from entering the area.
Another type of fence is mesh fencing. This fence is considered strong, long lasting, difficult to see and easy to install. The fence is made of a series of 10.16 cm2 UV resistant polyethylene mesh. Each strand has a breaking strength of 79.37 kg. Mesh is stretched 6.096 m between poles that are used to support it. The entire area that needs to be protected must be enclosed in order for the fencing to be effective. This fencing is considered very effective because deer have relatively poor vision and depth perception. The barrier and accessories are black so deer cannot judge where the fence starts or stops. Deer are scared of the fence and run around its perimeter but usually do not try to jump it. This fence provides a humane and discreet barrier that keeps deer out of sensitive areas without relying on chemicals or electricity.
Electrical fences (Figure 4-207) are easy to erect, repair and
maintain. Temporary electrified fences are simple, inexpensive and
useful. Baiting the fence with peanut butter or apples enhances
the effectiveness of electrified fences. Deer are attracted to these
fences by appearance or smell, and are lured into contacting the
fence with their noses. The shock trains the deer to avoid the fenced
area. Permanent high tensile electric fences provide year-round
protection from deer and are best suited to orchard crops. These
designs are best used under light deer pressure or for relatively
small areas. Low profile fences may not provide adequate protection
especially in the winter when snow restricts deer from using alternative
food sources. Check local bylaws to determine if electric fences
can be used on a property.
Figure 4-207. Deer fencing
(Ontario Soil and Crop Improvement Association)
Frightening deer using scare devices is effective and economical in some situations, particularly when they first become a problem in the orchard. Once deer establish a pattern of movement, it is difficult to get them to change. Propane cannons, cap exploders, strobe lights, sirens, fire works and gunfire are temporary methods of scaring off deer. However, deer often become accustomed to these tactics within a week or two, even when the devices are occasionally moved. Scare devices are usually a short-term solution. Some growers use dogs to help scare deer. Dogs can be contained in an area using invisible fencing, and they chase deer out of their territory. Large aggressive dogs work best for this - a family pet may not provide adequate protection.
There are two types of repellents used for deer - contact and area repellents. repellents are applied to the plants and repel by taste. Area repellents are most commonly used in orchards and are applied near the plants to be protected and repel deer by smell alone. Some area repellents include suspending bars of hand soap to the trees or hanging bags of human hair from the tree. Some growers report the use of Surround crop protectant containing kaolin clay acts as a deterrent to deer feeding while getting trees established. These repellents may only be a temporary solution to the problem.
During the hunting season, problem deer in orchards can be hunted by licensed hunters. Agricultural deer removal authorization is another way of managing deer populations. Applications are obtained from the MNR to hunt outside of the normal sport hunting season. These permits are used to harass and/or remove deer causing significant agricultural damage, when other reasonable methods to prevent damage are ineffective. Only those animals damaging crops can be removed. Orchardists may apply for an agricultural deer removal permit through the local MNR district office. Applicants are normally required to document and describe all other non-destructive attempts to control a damaging population of deer. Applicants must meet certain criteria and a site visit is usually completed. Authorizations are closely controlled and complement local deer management objectives. Deer removal authorizations cannot be used to provide recreational out-of-season hunting opportunities or personal gain.
Avoid planting orchards near pine plantations, a favoured habitat of crows. A variety of options are available for control including acoustical repellents, visual repellents, and physical exclusion. For more information refer to OMAFRA Factsheet 98-035, Bird Control on Grape and Tender Fruit Farms.
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