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Chapter 5: Wildlife Damage Management

5.1 Deer

5.1.1 Nonchemical Alternatives

A vegetable grower can use a variety of nonchemical alternatives to reduce deer damage to crops. These techniques fall into three primary categories: exclusion, population reductions, and habitat modification. Fencing is the most common exclusion technique used to prevent deer damage. Woven-wire designs are the most effective physical barrier, with high-tensile, woven-wire fencing providing the ultimate in protection and durability. Deer can be successfully eliminated from large areas with an eight to ten foot high woven-wire fence. The advantages of this design are its effectiveness and low maintenance requirements after construction. Disadvantages include the high initial cost and the difficulty in repairing damaged sections.

A variety of multistrand, high-tensile, vertical, or sloped electric fence designs may effectively exclude wildlife. Electric high-tensile fences can be complete physical barriers, or more often, act as psychological deterrents. Deer can be excluded from crops with a five to six foot electric fence, even though they can easily jump over fences of this height. The most frequent reasons why electric fences fail to prevent deer damage include: the selection of an unsuitable fence design, the failure to install fencing according to specifications, and inadequate maintenance. High-tensile electric fences are more easily repaired than conventional fences, and may cost half as much as eight to ten foot woven-wire designs. Disadvantages include the need for frequent monitoring and vegetation control to maintain shocking power. Single-strand electric fences, combined with cloth strips treated with deer repellents or aluminum foil tabs coated with peanut butter to act as an attractant, and attached at three to four foot intervals along the fence, have successfully reduced summer deer damage to vegetables. High-visibility, electric polytape fences on fiberglass stakes provide another low-cost, portable design that can effectively reduce deer damage to vegetable crops.

Posting of private lands reduces the opportunity for sportsmen to harvest antlerless deer. Deer populations are regulated through the removal of breeding-age does. Growers who experience recurring deer damage should invite hunters to their property and mandate that they fill an antlerless tag (if available) before harvesting a buck. Reducing deer numbers on a unit-wide basis may lower crop losses. Deer depredation permits issued on a farm-by-farm basis have not controlled crop losses in other states.

Deer problems are most severe in fields near escape or resting cover. Mowing or removing brush in fields adjacent to crops may make the sites less attractive for deer and other problem wildlife. Some growers have experimented with lure crops to draw deer away from important harvestable fields, however, these efforts have had mixed success.

5.1.2 Repellents

Repellents may be cost-effective for controlling wildlife damage when light to moderate damage is evident, small acreage is damaged, and only a few applications will be needed for adequate control. If these three conditions are not satisfied, it is best to look at the cost-benefit ratios of alternative control measures.

With the use of repellents, some damage must be tolerated, even if browsing pressure is low. None of the existing repellents provide reliable protection when deer densities are high. Repellents should be applied before damage is likely to occur, when precipitation is not expected for 24 hours, and temperatures will remain between 40° to 80°F for that period. Hand-spray applications may be cost effective on small acreages, while machine sprays will reduce costs for larger areas. If the materials are compatible, spray costs may be reduced by adding repellents to pesticide sprays. If browsing pressure is severe, a long-term damage management program should be implemented. Such a program should include potential habitat modifications, reductions in animal numbers, and an evaluation of fencing alternatives.

5.2 Woodchucks

Woodchucks are game animals in New York and can be hunted throughout the year without limit. A hunting license is required to harvest woodchucks. Woodchucks causing damage can be destroyed without a license under New York Conservation Law. Consult your regional Department of Environmental Conservation (DEC) office if you have questions about a specific situation.

Growers have usually relied on lethal controls to reduce woodchuck damage. Spring is the best time to use lethal controls, because adults are active and young animals may remain within their burrow at this time. In addition, burrows are more evident before annual vegetation conceals their entrances, and other wildlife are less likely to use burrows as shelter at this time.

Shooting or trapping methods can be used to remove problem woodchucks from fields containing edible crops. It may be illegal or unsafe to shoot woodchucks under some circumstances. Woodchucks can be captured using #2 leg-hold traps, #160 or #220 body grips, or live traps baited with apples and set near burrow entrances. Traps should be checked at least twice daily. Only live traps should be used where pets or livestock might be inadvertently captured.

Lethal controls have been reported to have limited success in controlling woodchuck populations. Twenty-eight percent of the burrows fumigated during one study were reoccupied within two days, and 83 percent of the burrows were reoccupied within two weeks after treatment. The rapid reoccupation of burrows may have resulted because the treatment was applied during the day when woodchucks are least likely to be inside burrows and because more than one animal may use a burrow system. Similarly, shooting and trapping methods will not eliminate woodchucks from a farm. In one Pennsylvania study, 1,040 woodchucks were removed from a 600 acre site over four years without significantly affecting the population's size.

Fencing can be effective at reducing woodchuck damage. Woodchucks may be excluded from small areas with a four-foot-high hardware cloth fence with the bottom buried ten to 12 inches, plus an electric hot-shot wire located four- to five- inches-high and an equal distance away from the outside of the fence. Electric, high-tensile deer fences may be modified to exclude woodchucks by adding additional wires at five to six inch intervals up to 18 inches high.

There are no products currently registered with the EPA for use as woodchuck repellents.

Modification of habitats in and around fields can help reduce their attractiveness to woodchucks, and can increase the effectiveness of other control techniques. Elimination of brush piles and overgrown areas will facilitate the discovery and treatment of burrows. Unfortunately, elimination of these areas may also eliminate valuable habitat for other wildlife. There is no research that indicates supplemental plantings can draw woodchucks away from more valuable crops.

5.3 Rabbits

Cottontail rabbits are found throughout New York State, excluding the central Adirondacks. Most rabbit damage occurs during spring or early summer when succulent new plants are available in crop fields or gardens.

Fencing can effectively protect small areas of high-value vegetable crops. Two-foot-high poultry-wire with 1- to 2-inch openings can adequately exclude rabbits. The fencing should be supported every six to eight feet with heavy wooden stakes or metal posts. It is critical to keep the lower edge of the fence tight to the ground, as rabbits will usually not dig under a fence, but will try to squeeze through existing openings or loose areas. If fences are installed in the spring and removed and stored in a dry place during the fall and winter, the materials may last five to ten years.

Cottontails are game animals in New York, and sport hunting can be used to effectively lower rabbit numbers in rural areas. Rabbits causing damage may be destroyed without a permit under existing New York State Environmental Conservation Law (Title 5, Section 11-0523). In more urban locations where hunting may not be possible, rabbits can easily be captured in box traps or commercial wire cage traps. Permits from DEC will be required to trap and transport live cottontails, and it is best to contact your Regional DEC office before capturing or killing rabbits. Live traps can be baited with apples or corn, and once a rabbit is caught in a trap, its lingering scent will often attract other cottontails. Putting a few cottontail droppings in a trap along with the bait will enhance the trap's effectiveness. Rabbits are usually most active just after sunset and just before sunrise. Live traps should be set prior to these peak activity periods.

One repellent is commercially available to protect carrots from rabbit damage. There are no research reports available to indicate the effectiveness of these materials for preventing rabbit feeding.

Cottontails require dense vegetation near feeding areas for protection from predators. Overgrown ditches, stream banks, fence rows, or brush piles within or near crop fields may harbor abundant rabbits. Mowing, cutting brush, and removing brush piles or overgrown areas may effectively control cottontail problems.

5.4 Raccoons

Raccoons like sweet corn when kernels are at the milk stage and will dig holes in watermelons to scoop out the contents. Foraging usually takes place at night.

Raccoons are protected fur bearers in New York State, with established hunting and trapping seasons. All local laws or ordinances must be followed, and your DEC Regional office should be contacted before implementing lethal raccoon control.

Exclusion is the best method for preventing or reducing raccoon damage. Sweet corn or melon fields can be protected with double strand electric fences with wires five and ten inches above ground. Fences can be turned off during the day, or left on continually if woodchuck damage is also a problem. Fences should be installed at least two weeks before sweet corn reaches the milk stage, so the raccoons do not develop foraging habits.

No frightening methods have effectively reduced raccoon damage to sweet corn for more than short periods of time. Lights, radios, dogs, scarecrows, streamers, aluminum pans and lids, etc. have been tried with little success. Also, no toxicants or fumigants are currently registered for raccoon control. The repellents tested to date have also been ineffective.

Raccoons can be easily captured in traps. Live traps at least 10 by 12 by 32 inches in size and constructed of sturdy metal can be baited with marshmallows to reduce captures of nontarget species. Environmental Conservation Law permits only licensed Nuisance Wildlife Control persons or Wildlife Rehabilitators to transport live-captured animals, so the landowner must euthanize raccoons caught in cage traps or release them at the site of capture. Raccoons may also be captured in #1.5 leg-hold traps, and #160 or #220 body gripping traps can effectively catch raccoons in bait boxes. Body gripping traps are designed to kill quickly and should not be used in areas where there a chance of catching nontarget animals.

Due to the spread of raccoon rabies in New York, contact with raccoons should be minimized. Animals shot or captured in traps should only be handled with rubber gloves, and all traps and equipment should be disinfected with a bleach and water solution. Carcasses should be cremated or deeply buried. Field workers should be warned to avoid any wildlife which acts abnormally, as rabies may spill over into other mammal species.

5.5 Birds

5.5.1 General Information

Agricultural regions throughout North America are susceptible to bird damage. Bird species which impact vegetable growers fall into two broad categories: resident and migratory. Resident birds (i.e., crows, turkeys, etc.) may inflict low levels of damage throughout the grain-ripening period or pull up sprouting grain in the spring. Migratory species (i.e., starlings, blackbirds, etc.) often forage in large flocks and can cause severe corn losses in a few days.

All birds, except feral pigeons, house sparrows, and starlings, are protected by the Federal Migratory Bird Treaty Act. However, Section 21.43, Title 50 CFR, states that, "A Federal Permit shall not be required to control red-winged, rusty, and Brewer's blackbirds, cowbirds, all grackles, crows, and magpies when found committing or about to commit depredations upon ornamental or shade trees, agricultural crops, livestock, or wildlife, or when concentrated in such numbers and manner as to constitute a health hazard or other nuisance. . ." When considering harassment or lethal methods to control problem birds, local ordinances must still be followed, so it is best to consult with local law enforcement authorities or Regional DEC offices if you have questions concerning specific situations.

5.5.2 Exclusion

Netting is the most effective method for controlling bird damage. The cost of bird-proof plastic netting varies considerably with the type, manufacturer, and quality. The initial cost of netting may be quite high, but the cost can be prorated over the three to ten year life expectancy of the material. There is a high labor cost for installation and removal of netting, and this method is usually cost-effective only for the most valuable crops.

Monofilament lines have been used in several spacings and configurations to reduce bird damage at landfills, fish hatcheries, public parks, and agricultural fields, although species responses are quite variable. For example, gulls, crows, and sparrows appear to be particularly sensitive to lines and have been successfully repelled. Usually lines are only practical for small plots or home gardens.

5.5.3 Auditory Frightening Devices

Broadcasts of recorded distress or alarm calls have been used successfully to drive birds from fields, orchards, and roosts. The sounds of a recorded propane explosion and distress calls were evaluated for reducing night heron damage to aquaculture ponds. The herons completely habituated to the cannon recording after six nights of exposure. However, more than 80 percent of the birds left the pond when the distress call was used, and no habituation occurred after six months. The use of recorded distress or alarm calls may have additional applications for bird management, but most calls are species specific, so growers must identify birds causing the damage.

Other bird-control methods (bangers, crackers, poppers, bombers, sirens, etc.) rely on perceived danger for their effect. These techniques have been effective for short-term control, as scare devices that produce sounds other than alarm/distress calls have no persistent effect on space use or food intake of birds. Best results are obtained when: sounds are presented at random intervals; a range of different sounds are used; the sound source is moved frequently; sounds are supported by other methods, such as distress calls or visual deterrents; and sounds are reinforced by real danger (i.e., shooting). Experiments conducted to date indicate that ultrasound probably cannot be heard by birds.

5.5.4 Visual Frightening Devices

Eye-spot balloons were reported to reduce damage to citrus groves. Balloons may be a more acceptable bird control practice in suburban areas where sound devices could lead to conflicts with neighboring landowners; however, the effectiveness of balloons appears to depend on the bird species causing the damage, and results are variable.

Reflecting tapes placed three to seven yards apart were effective in protecting small fields (one acre) of sweet corn, millet, and sunflowers from bird damage. However, reflecting tapes spaced three to four yards apart did not protect blueberries from robin or starling damage. Reflecting tape requires substantial labor for installation and maintenance.

5.5.5 Cultural Practices

Fields near convenient perches, such as snags or power lines, may be prone to increased losses. Grass and weed control may reduce the numbers of certain seed-eating bird species. If possible, it is best to establish new vegetable fields away from cover or perch sites or to remove these attractive habitat features from areas next to existing plantings.

Insect control may reduce the number of birds feeding in corn fields. European corn borers attract red-winged blackbirds to sweet corn fields, and controlling corn borers will result in decreased bird damage to corn ears. Blackbirds generally feed on insects in corn fields during the silking period. Red-winged blackbirds accounted for more than 90 percent of bird observations in sweet corn fields in the Hudson Valley, and corn damage by red-wings did not occur until the ears reached the milk stage. Avian damage increased rapidly once kernels reached this stage, so advancing harvest by a few days can greatly reduce losses.

Cultivars of corn differed substantially in susceptibility to bird damage in free-choice trials. Husk coverage of the ear (expressed as husk weight or length of husk extension beyond the cob tip) accounted for about 68 percent of the variation between cultivars in aviary tests. In general, the most susceptible cultivars received about 2 1/2 times more damage than the least susceptible. However, stage of kernel maturity at the time of bird damage influenced the relative resistance of cultivars, as differences between cultivars were less pronounced at late stages of maturity.

5.5.6 Management Guidelines

The success of most bird damage management activities depends upon the interest and persistence of the field person conducting the control efforts. Field staff should monitor bird numbers and species present. If scare devices are warranted, they must be functional from shortly before sunrise until sunset. Birds quickly habituate to most frightening techniques, but the period of effectiveness can be lengthened by frequently moving scare devices, and reinforcing the stimuli with real danger (shooting), where legal and practical. Combining a number of different methods usually results in greater success than relying on a single technique.

Damage mitigation measures may only be cost-effective early in the harvest season when birds are concentrating their feeding on early-ripening cultivars. Growers should carefully monitor these fields, so timely and appropriate control efforts can be implemented. Control measures often become cost-effective when large flocks of migratory birds move into the area. In particular, migratory blackbird flocks can inflict substantial damage during short time periods. Again, careful monitoring is necessary to determine the timing and potential amount of crop loss. Growers should decide whether or not to attempt to control damage, and which techniques are appropriate, based on their estimates of potential losses.

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Maintained by Abby Seaman, New York State IPM Program. Last modified 2018.


This information is based on the Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production, Cornell Cooperative Extension.

Authors

Stephen Reiners, SIPS Horticulture Section, Cornell AgriTech at Cornell University; Editor; cultivar selection and fertility
Lynn Sosnoskie, SIPS Horticulture Section, Cornell AgriTech at Cornell University; weed management
Bryan Brown, NYSIPM Program, Cornell AgriTech at Cornell University; weed management
Paul D. Curtis, Natural Resources, Cornell University; wildlife management
Michael Helms, Pesticide Management Education Program, Cornell University; pesticide information
Margaret T. McGrath, Plant Pathology, Long Island Horticultural Research and Extension Center, Riverhead, NY; disease management
Brian A. Nault, Entomology, Cornell AgriTech at Cornell University; insect pest management
Abby Seaman, NYSIPM Program, Cornell AgriTech at Cornell University; integrated pest management

Special Appreciation

Special appreciation is extended to the following for their contributions to this publication: George S. Abawi, Robin Bellinder, Helene R. Dillard, Donald E. Halseth, Michael P. Hoffmann, Andrew J. Landers, Curt Petzoldt, Anu Rangarajan, Anthony M. Shelton, Christine D. Smart, John Wallace, and Thomas A. Zitter.