Vertebrate Pest Management

USDA Wildlife Services staff are available to assist with a variety of wildlife damage issues. Their telephone number for New Hampshire & Vermont growers is (603) 223-6832. For growers in Connecticut, Massachusetts and Rhode Island: (413) 253-2403. For Maine: (207) 629-5181. The website is http://www.aphis.usda.gov/wildlife_damage. Trapping is often highly regulated; laws are restrictive and may be complex. Environmental Police Officers enforce trapping laws. Know the current laws and regulations before trapping any wildlife. Reductions in animal numbers by lethal methods fail to provide a long-term solution from wildlife damage in the absence of habitat modifications and exclusion methods. Most nuisance wildlife will repopulate areas soon after control efforts have ceased. Habitat modification and exclusion methods often require more expense and initial effort, but these methods will result in more durable damage prevention.

Deer

White-tailed deer are common in New England, and sweet potato leaves and vines are among their most preferred foods. In some areas, they heavily attack pumpkins, both the plants and fruit. We also see damage to butternut squash, lettuce, and occasionally tomato and other vegetable plants. They are very active at night, but during the summer they are almost as active during the day.

Fencing: Permanent mesh fencing can keep them out if it is 8-10 feet high. Such fencing restricts vehicle movement, so carefully consider turning distances, entrance locations, and gate width before making an investment in permanent fencing. Temporary electric fencing is relatively inexpensive and simple to set up. It can work very well if you bait it immediately after erecting it. Even a single electric strand at 36-40" can work if the deer have other feeding options. White electric tape is especially visible and works well in this application. The most common method to bait an electric fence for deer is to apply peanut butter to strips of aluminum foil and fold them (sticky side in) over the fence at about a 40" height, at intervals of about 30-50 feet. By licking the tasty treat they can smell, deer quickly learn that the fence can hurt them, and they keep away. Usually, the baits do not need replenishing if they are used for less than one growing season.

Repellents for deer are designed to work by odor or taste. Most commercial products are not labeled for direct application to vegetable crops.

Shooting is one option that growers may consider, but the rules vary greatly from state to state. Sometimes officials will readily give out permits to shoot offending deer. Shooting is not as effective as fencing and brings on issues of safety, neighbors, and farmer image. Deer are protected species in all New England states, so check with state Fish and Game authorities or USDA Wildlife Services staff before shooting.

Birds

Most birds in New England that are pests of vegetables are species with either partial or complete legal protection. State, federal, and international laws/treaties are involved in their protection. This limits some of our management options. Crows and ravens often pull out seedling corn plants, to reach and consume the seed. They, along with blackbirds and starlings, frequently attack milk stage corn, especially in varieties where the ears are not well covered by the husks. Turkeys feed on kale, collards, lettuce, and mesclun mix. They also peck both green and ripe tomato fruit. Canada geese like to eat grasses and winter rye, and sometimes corn. Occasionally birds cause losses by defecating on the crops. This is most common when open containers of product are placed in an open shed or barn, where English sparrows can perch in the rafters above. In that situation, growers can install netting to exclude birds from the rafter area or repellant spikes to discourage perching. Canada geese defecating while grazing on grassy weeds can be an issue on low crops that are eaten fresh, like lettuce and spinach.

There are a variety of devices designed to manage bird problems.

Netting is one possibility but is most appropriate for high-value perennial crops, not most vegetables. Some of the insect and hail netting designed to protect mesclun mix and other low crops can be supported by wire hoops and stops turkey feeding. 

Taste Repellents. Some taste repellents are available (e.g. methyl anthranilate) for use on some crops, but they are applicable to few vegetable crops and have variable results in our area. An exception is 9,10-anthraquinone, sold as Avipel. It is registered as a seed treatment on corn to keep birds from walking down the rows and pulling out the seedlings. Currently, it is registered in Maine, Vermont, New Hampshire and Massachusetts.

In states where anthraquinone is not registered, growers have used two methods to reduce seedling pulling by crows and ravens. One method is to set up tomato stakes in a zig-zag pattern on a recently planted sweet corn field. Attach fishing line to the stakes. This seems to deter crows from landing. When the seedlings are large enough that the birds can’t pull them out, you can reel up the fishing line, retrieve the stakes and put them in your next planting. Another alternative is to plant sweet corn into a low standing stubble. It can make the young plants harder for the crows to spot.

Scare devices can be relatively effective, especially on flocking species. All birds become habituated to scary noises, especially if they are used alone and constantly. Therefore, incorporating variability (in sound, location, etc.) is important to being successful with scare devices. The University of New Hampshire resource Bird Damage Prevention For Northern New England Fruit Growers covers most scare devices. Two relatively new ones not covered in that publication are Air Crow and laser lights. Air crow is a colored nylon tube/scarecrow attached to a blower. When in use, it moves constantly and can be quickly turned off when not in use. Set it in a location that makes it visible. For tall crops, that might be on a bin or stand. As with other scare devices, it is most effective when combined with other methods. Laser bird deterrents mounted on a firm mast are available. Coverage area depends on product, site, light, and weather conditions. Some New England vegetable growers have been very happy with the results scaring various birds, despite the high cost.

Auditory bird scare devices can be fairly effective, especially if the noises they create are varied. Automated propane cannons can be effective for a relatively short time, but are very annoying to neighbors, customers, and farm workers. In New England, automatic cannons have been the source of several serious disputes with neighbors. Screamers and bangers are auditory devices that are fired from a pyrotechnic shot launcher (looks like a plastic handgun). They can cost $2.50 or more per shot but can occasionally be helpful to move out a flock of birds. Regulations cover the purchase and use of these devices. Be sure to check local regulations about their use before you begin.

Silhouettes of coyotes or other predators don’t work very well to scare birds (or other vertebrate pests of vegetables). Effigies are slightly more effective, especially those that employ movement. They are still more effective if you regularly move them to different spots. If you combine them with auditory scare devices, the effectiveness usually increases.

Some growers employ scare-eye balloons to protect sweet corn from pecking. Growers report that the light colored balloons work better than the dark ones. There are some larger ones with “holographic” eyes that seem to follow you as you walk by. Growers have had relatively good results with them. With all of the balloons, it is important to suspend them from high poles 2-5 feet above the crop.

Shooting is rarely effective at controlling bird problems. The main effect is scaring away the survivors. There are local, state, and international laws that affect if, where, and how shooting may be employed.

Rodents

Rodents are distinguishable by their teeth. They have sharp, opposing incisors plus strong molars to grind up material. Between the incisors and molars, there is a broad gap with no teeth.

Woodchucks

Non-lethal Measures. Frightening devices don’t seem to be effective at deterring woodchuck feeding. Although some taste repellents are available, they are not very practical for vegetable crops that people will be eating. Fencing can be very effective but restricts vehicle movement. Also, if you depend on fencing, be sure the woodchuck burrow is not inside the fence. Since woodchucks can climb and burrow, the most effective alternative is electric fencing. An effective combination is one wire 4" off the ground and a second at 8 or 9" high. Dealers offer a wide variety of plug-in, battery, and solar powered UL-approved chargers. Keep the fence clear of any obstructions or vegetation that might short out the electric pulses.

If you use non-electric fencing, buy a mesh size smaller than 2"x2" inches, especially close to the ground, as young woodchucks can sometimes squeeze through that mesh size. Common chicken wire rusts away quickly—the woodchucks may push through it by the second growing season. Non-electric fencing should have some means of preventing the woodchucks from burrowing underneath. Fences can be buried to a depth of 10-12". Or, the lower 1 ft of fence can be bent 90° outward, to form an "L", then laid on the ground and secured by anchoring the "L" into the ground. Another option is laying an 18" wide strip of galvanized fencing on the ground below the fence, keeping the vertical fence flush with it. Non-electric fences need to be at least 3 feet high. Bending the top 12-15" outward at about a 45-degree angle will help deter them from climbing a non-electrified fence. Don't neglect the gate. That is often the spot where defenses are the weakest. If animals try to burrow underneath, install a board dug into the ground and flush with the bottom of the gate, or lay down a length of fencing as described above.

Live trapping is a possibility in some situations, but it carries risks. Small details in setup make big differences in the success rate. If a carrier of rabies were trapped, handling it could be a risk to any non-vaccinated person who was exposed. Trapping and translocating a woodchuck from its home is subjecting the “humanely trapped” animal to a prolonged, very stressful ordeal that often ends in its death. Suitable habitat is farmland with open fields and an abundance of short grasses. Farmers or gardeners are not likely to agree to releasing animals on their property, and woodchucks are not woodland creatures. In some New England states, laws prohibit the practice of transporting and releasing trapped animals.

The most effective technique is to place the trap directly at the burrow entrance and use a barrier of boards or other material to direct the animal into the trap as it leaves its burrow. No bait is needed in this situation. Trap placement elsewhere is much less effective, but sometimes the woodchuck can be enticed inside with fresh apple slices or fresh carrots or lettuce. Change baits daily.

Lethal Controls. Use lethal controls cautiously, after careful thought. They can end up killing non-target animals. Gas cartridges are cardboard cylinders filled with slow-burning, asphyxiating chemicals. Locate an active burrow, and treat when you are sure the woodchuck is inside. Find and close all but one entrance, and prepare a sod plug for the opening. Attach the cartridge to a 3 foot-long branch, light the fuse, and place it well inside. Immediately seal the entrance. Most failures with cartridges are from the fuses going out (often because loose dirt covered them, or they were thrown). Sometimes they fail because the woodchuck was somewhere else when the burrow was fumigated. Upon its return, it just re-opens the burrow. Never use a gas cartridge near flammables or under a wooden structure.

Conibear traps are body-gripping steel traps that almost instantly kill an animal that tries to move through. If a pet or other non-target animal walks through one, there is no second chance. Use these traps only where you are certain the intended target is the only animal that can enter. They are usually placed just inside the burrow, to trap the occupant as it enters or leaves. Conibear sizes 160 and 220 are appropriate sizes for woodchucks. These traps are dangerous and most states require users of them to obtain a permit or license. Contact your state animal authority before attempting to use a conibear trap.

Shooting is an option that has a low risk of harming non-target animals if done carefully. In many New England states, woodchucks can be shot by anyone with a hunting license, or by farmers on their own property, protecting their crops. In most New England states, there is no closed season on woodchucks. A .22 caliber rifle with hollow point cartridge is the most commonly employed weapon for woodchuck control. When shooting, take extreme care that the area is safe for a shot. A .22 caliber long rifle bullet can travel nearly a mile if it does not strike something first. They easily ricochet off hard surfaces.

Voles

Voles can attack a wide range of plants. In New England, they have been reported attacking tomato, asparagus, potato, sweet potato, carrot, and other vegetables. Grasses are especially favored foods for several species of voles. There are 4 vole species (meadow, southern redback, rock, pine) that can cause problems in New England, but most suspicion falls on meadow voles and pine voles. Pine voles primarily live and feed in tunnels underground and readily attack root crops: carrot, beet, potato, and sweet potato. They have very short tails, never longer than their hind feet. Meadow voles largely live above-ground and have tails that are longer than their hind feet. Voles have less prominent eyes than mice, and their ears are buried in the fur. Mice have prominent ears.

We have few options to manage pine voles on vegetable farms. Problems are most common in soils that are adjacent to woodlands or orchards. Soils that are poor for pine voles are those that are commonly waterlogged, have very high clay content, or are almost entirely sand. Tunneling is difficult in those conditions. Meadow voles mostly live above ground and often chew off plants just above the soil line, especially if there is a lot of vegetation to hide them. Weedy fields and field edges are common sites of attack. Sometimes voles attack when very young plants are still in liner or plug trays on the ground in a high tunnel. Meadow voles have an extremely high reproduction rate, so their populations can rebound rapidly after controls are implemented.

Voles prefer areas with good cover, so maintaining good weed control is important to reduce the risk of vole problems. Piles of debris placed right next to high-risk crops (like a high tunnel full of transplants) are invitations for vole problems. Mulches, including organic mulches, woven blankets, or plastic mulches, can encourage vole problems.

Rodenticides: There are rodenticides registered for use against voles in orchards, fruit groves, nurseries, and highbush blueberries. Currently, there are no rodenticides registered for use in vegetable fields. There are several rodent baits registered for use in and around buildings (commensal use), but are largely intended for use against mice and rats and the baits are formulated to appeal to those species, not voles. Contact your local Extension agent or USDA Wildlife Services to discuss the use of a rodent bait targeting voles around high tunnels or farm buildings.

Be very cautious about using the second-generation anticoagulants—brodifacoum, difethialone, and bromadiolone. These materials (especially brodifacoum) have been found in an amazingly high percentage of dead, sick, or injured predatory birds and predatory mammals in the northeast states. EPA responded to this problem by drastically reducing the availability of brodifacoum products for use by non-licensed applicators, but it is still available for licensed applicators to apply, in and around buildings. If pets or wildlife can reach the bait, they can be poisoned.

In most cases, rodenticide labels state that rodent baits must be used in bait stations. In part, this is to reduce the risk of direct poisoning to domestic animals. However, secondary poisoning can occur when a target pest becomes weakened or dies as a result of eating the bait, then a second, non-target animal eats the target pest and is poisoned.

Rodenticide labels are usually available to examine at the manufacturer’s website. Common manufacturers that include some field-applied products registered in New England include:

• Bell labs http://www.belllabs.com/
• Bonide https://www.bonide.com/
• Liphatech http://www.liphatech.com/ 

Make sure any rodenticide you plan to apply is registered in your state. See Pesticide Registration under Pesticide Safety for more information.

Trapping is a possibility for meadow, redback, and rock voles, but it isn’t very practical. Tiny details have a major effect on trapping success. In a situation where high-value plants are concentrated and damage is significant (e.g., high tunnels full of plugs or transplants) careful trapping might help. Vole tubes can be effective traps. Using scrap lumber, create a 16-18" long narrow tube, whose rectangular interior dimensions fit a standard mousetrap, leaving enough room for the spring bar to clear the ceiling. For most traps, that inside measurement would be 2’’ wide and 2.5” high. At the center of one side, leave an opening large enough to easily insert a mouse trap. Consider placing two traps in a tube, each one with the trigger facing its respective end. Then gently set the tube in the desired location and place a piece of cardboard to cover the side opening. No bait is needed. Voles like traveling in protected runs and this catches them as they try to use an inviting runway. It keeps the trap safe from your cat or dog, and your workers’ toes. Tubes can be placed along established paths between the trays of plug plants.

Vole Problems in High Tunnels/Greenhouses. Growing vegetables inside structures presents a different set of regulations, compared to outdoors. The use of rodenticides is one area that is not very clearly defined in this situation. Many rodenticides are labeled for “commensal” (in and around buildings) rodent control, not for use on or around a crop. When you grow a crop inside the structure, that brings up new legality issues. Also, commensal rodenticides are typically formulated to entice rats and mice, not voles. Cats find warm greenhouses and high tunnels especially inviting, and this behavior increases the risk of poisoning them if you use rodenticides in or around those structures. As described above, secondary poisoning is a significant concern with some rodenticides. Avoid using rodenticides inside high tunnels or other structures where food crops are grown for harvest unless the product is specifically labeled for this use and for the pest(s) you are trying to control.

For a greenhouse in which you plan to grow vegetables, it is possible to reduce the chances of having vole problems by using ¼ inch mesh hardware cloth to seal all openings at or near ground level. Bury the edges well. High tunnels are much harder to protect from vole entry. In both high tunnels and greenhouses, control weeds well inside. Keep the vegetation around the structures well-mowed or controlled with herbicides. 

Other Rodents

Gray squirrels commonly raid ears of corn, especially in fields that are close to woods. Damage is sporadic, so controls are usually not warranted. Gray squirrels are protected species in all New England states.

Mice tend to be seed eaters, though some will feed on fruits when given an opportunity. The white-footed mouse is a common New England species that frequently moves into buildings, especially in fall and winter. Usually, we do not see evidence of them attacking vegetable plants. Mice have prominent ears and eyes, while voles tend to have smaller ears and less prominent eyes.

Muskrats are rodents that are strongly associated with ponds, marshes, and slow rivers. They eat aquatic plants, but occasionally attack corn, beans, wheat, or oats that are growing adjacent to wetlands. Damage is uncommon, so controls are not usually warranted.

Rats (Norway, roof) occasionally attack harvested vegetables stored in containers indoors, but rarely are reported attacking plants in the field. Rat control can be very demanding. It requires eliminating food sources, plugging holes in walls, and careful use of traps and/or rodenticides. Rats are notoriously reluctant to try new foods (like rodent baits), and resistance to rodenticides is a problem. Contact your local Extension specialist for additional resources on rat control in indoor farm settings.

Lagomorphs (Rabbits & Hares)

Rabbits and hares are close relatives of rodents. Cottontail rabbits are the most common species attacking vegetables. We have two species here: New England cottontail and the larger Eastern cottontail. They eat a wide variety of vegetable plants (carrot, pea, bean, beets, lettuce, spinach, and others). They do not tend to feed on corn, squash, tomato, cucumber, or potato. They eat many cut flowers (e.g., tulips). European and snowshoe hares can be found in western Connecticut and northern New England, respectively, but these are not usually associated with damage to vegetables. 

The most common form of lagomorph control is fencing. Two-foot high fencing with 1" mesh is sufficient if it is buried slightly into the ground. Chicken wire can work, but very young rabbits can sometimes squeeze through. Electric fencing designed for woodchucks or raccoons is often also effective against lagomorphs and less expensive than erecting mesh fencing.

Thiram is a fungicidal seed treatment that also acts as a taste repellent against lagomorphs, but it is not labeled for use on vegetables other than as a seed treatment. Shooting may be an option in some situations, but the aforementioned species are protected, so be sure to check first on state regulations and follow gun safety practices. For rabbit control, .22 rimfire rifles are commonly used.

Carnivores 

Raccoons

Raccoons are a common presence and are especially active at night. Before the raccoon strain of rabies moved through New England in the mid-1990s, raccoon damage to sweet corn was a very serious problem, and many growers used electric fences to protect sweet corn in the milk stage. Today sweet corn damage from raccoons is less common. Raccoons also attack cantaloupe and watermelon fruits.

Fencing. The most common and effective control for raccoons is electric fences, with one wire at 6" height and a second at 12". Sometimes a single wire at 6" works well. Be certain that vegetation is cleared from the fence, or it will reduce the shock an animal receives when it contacts the wire. Fencing will limit vehicular traffic, but temporary clip-on gates are easy to install.

Trapping. Some farmers employ trapping, but it can be difficult and time-consuming to do properly and may be subject to local and/or state laws. The raccoon is a protected species, and the rules vary state to state. Live trapping requires a sturdy trap and an effective bait, e.g., sardines. Transporting trapped animals is illegal in some New England states. Leg-hold or lethal body-gripping traps can be effective but are dangerous for non-target animals, including humans and typically require permits or licenses. Contact your state animal control authority before attempting to use one of these traps. If you do use traps and need to move a dead raccoon, use rubber gloves. Raccoons can harbor the nematode Baylisascaris procyonis (“raccoon roundworm”) that can parasitize people. Raccoons can also be infected with rabies virus, which is lethal to people.

Other Carnivores

Opossums occasionally feed on sweet corn, and some fruits. They are omnivores that feed on carrion, as well as fruits and grains. They are more active at night than during the day. Electric fencing is the most appropriate control method.

Red foxes are common in New England and sometimes feed on ears of corn or cantaloupe fruits. We rarely get reports of significant damage. Foxes are valuable predators of voles and other pests, so we generally consider their presence beneficial. They are protected in all New England states.

Black bears are more common in northern New England than southern New England. Bears readily attack sweet corn and field corn in the milk stage. Damage often occurs in large spots in the middle of the field, where the bears pull down all of the stalks and are hidden from view. Since black bears are protected by laws, contact your state Fish & Game officials or USDA Wildlife Services staff for assistance if you have a bear problem.

Resources

Bird Damage Prevention For Northern New England Fruit Growers: https://extension.unh.edu/resource/bird-damage-prevention-northern-new-england-fruit-growers

Carpe Diem Technologies: www.carpediemtechnologies.com. Laser bird scare devices.

Dealing With Woodchuck Damage: https://extension.unh.edu/resources/files/Resource000562_Rep584.pdf

Managing Voles in New Hampshire Orchards and Highbush Blueberries: https://extension.unh.edu/resources/files/Resource003424_Rep4893.pdf

Orchard Equipment Supply Company (OESCO), Conway, MA: www.oescoinc.com.
1-800-634-5557. Bird netting supplies and support.

USDA Wildlife Service: NH & VT (603) 223-6832; CT, MA, RI (413) 253-2403. http://www.aphis.usda.gov/wildlife_damage/

Wellscroft Fence Systems Chesham, NH. www.wellscroft.com
1-855-327-6336.