Vertebrate Pest Management

USDA Wildlife Services staff are available to assist with a variety of wildlife damage issues, including voles. 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 or 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 inches 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 at 40 inch height, at intervals of about 30 to 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.

Taste repellants for deer actually work by odor, while others must be tasted to work. But none of these repellants are really applicable 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. Shooting also has safety issues.

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 and blackbirds, 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, 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. 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 repellants: Some taste repellants are available (methyl anthranilate for example) 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 (effective) as a seed treatment on corn to keep birds from walking down the rows and pulling out the seedlings. Currently (2017) 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 and change (sound, location, etc) is important to being successful with scare devices. 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.  A Canadian company called Carpe diem has been selling a system of laser lights mounted on a firm mast. Some New England vegetable growers have been very happy with the results scaring various birds, despite the high cost ($2500 or more).

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 launcher (looks like a plastic hand gun).  They can cost $2.50 or more per shot, but can be helpful occasionally 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 goes up.

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 successful 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

Woodchucks especially like to eat beans, peas, carrot greens, alfalfa, clover, and grasses.  They also eat cabbage, broccoli, tomato, dandelion, and other plants. There are few succulent plants that they won’t eat.  They don't seem to prefer corn.  They are most active early in the morning and late in the afternoon. They dig extensive burrows that are used as escape cover, shelter, or overwintering sites by many other animals.  Cottontail rabbits, skunks, raccoons, foxes, coyotes, snakes, weasels, and chipmunks are among the animals that use woodchuck burrows.  Woodchucks are also prey for foxes and coyotes, bobcats, fishers, eagles, and large hawks. Please consider these points before jumping to lethal control measures for woodchucks. Both lethal and non-lethal control options are available.

Non-lethal measures: Frightening devices don’t seem to be effective to deter woodchuck feeding.  Although some taste repellants 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 inches off the ground and a second at 8 or 9 inches high.  Dealers offer a wide variety of plug-in and battery 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 X 2 inches, especially close to the ground.  (The young ones 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.  You could bury the fence to a depth of 10 or 12 inches.  Or you could bend the lower 1 foot 90 degrees outward, to form an "L", then lay it on the ground and securely pin the L into the ground.  Another option is laying an 18 inch wide strip of galvanized fencing on the ground below the fence, and keep the vertical fence flush with it.  Non-electric fences need to be at least 3 feet high.  Bending the top 12 to 15 inches outward at about a 45 degree angle will help deter them from climbing non-electrified a 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 your 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 them 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 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 then, 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. This risky method requires permits or licenses in many areas, so check first before using this.

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 food for several species of voles. We have four 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 (not leg!). 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, or 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. If you use a mulch, it can encourage vole problems. This includes organic materials like grass clippings, woven blankets, or extruded materials like plastic.

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. A limited number of products might be legal for use (gray zone) in high tunnels and in and immediately around other buildings, but they may be of very limited use. There are quite a few rodent baits registered for commensal (in and around buildings) rodent control, but the term vole rarely appears on their labels. For the most part, commensal rodent control products are intended for mice and rats, and the bait is formulated to appeal to those species, not voles.

Be very cautious about using the second-generation anticoagulants (brodifacoum, difethialone, bromadiolone). These materials (esp. 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, in and around buildings. If pets or wildlife can reach the bait, they can be poisoned.

In most cases, the 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. But secondary poisoning can occur (brodifacoum for example), where one animal eats the bait and becomes weakened or dies. Then a second animal eats the target pest, and becomes a victim.

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:

There are many additional manufacturers that provide materials for commensal (in and around homes) rodent control. If you cannot tell if a rodenticide is registered for use in your state, check the registration list. Each New England state has a list of pesticides that are registered in that state for that year. Often the list is incomplete early in the year. In most states, that list is available through the state pesticide control division.

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 (high tunnel full of plugs or transplants for example) careful trapping might help.  In that case one or more vole tubes might be a good situation for a trap. Using scrap lumber, you create a 16 to 18 inch long narrow tube, whose rectangular interior dimensions fit a standard mouse trap, 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 a 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.  One spot to place a tube is where there is an established path 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” (means in and around buildings) rodent control, not for use in 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.

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.  Just outside, keep the vegetation well mowed or controlled with herbicides. 

Other Rodents

Gray Squirrels commonly raid ears of corn, especially if they are close to woods. Damage is sporadic, so usually controls are 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.  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 or slow rivers.  They eat aquatic plants, but occasionally attack corn, beans, wheat or oats that are growing adjacent to wetlands. Attack is uncommon, so it rarely warrants control.

Rats (Norway, roof) occasionally attack picked vegetables stored in containers indoors, but rarely are reported attacking the 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. Rat control in buildings isn’t the focus of this reference, so you’ll need to look elsewhere for details.

Lagomorphs (Rabbits and Hares)

Rabbits and hares are close relatives of rodents. Cottontails 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, potato. They eat many flowers (tulips for example). Good cover is especially important to help hide these animals from their many enemies. Western Connecticut has European hare, and northern New England has varying (snowshoe) hare, but these are not usually associated with damage to vegetables. 

We most commonly use fencing for lagomorph control. Two foot high fence with 1 inch 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 effective and less expensive than erecting mesh fencing.

Thiram is fungicide that is a taste repellant that works on rabbits, but it is not labeled for use on vegetables. Shooting may be an option in some situations, but these are protected species, so be sure to check first on state regulations. There are safety issues with shooting. We most commonly use a .22 rimfire rifle for rabbit control.

Rabbits strongly prefer to be in thick cover, so good weed control and mowing edges can help reduce the risk of damage.

Carnivores 

Raccoons                                              

Raccoons are a common animal that are especially active at night. Before the raccoon strain of rabies moved through New England (mid 1990’s), 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. They are most active at night.

Fencing: The most common and effective control for raccoons is using electric fences, with one wire at 6 inch height and a second at 12 inches.  Sometimes a single wire at 6 inches 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. Raccoon is a protected species, and the rules vary state to state. Live trapping requires a sturdy trap and an effective bait. Sardines are one bait that has worked. Transporting trapped animals is illegal in some New England states. Conibear (lethal body-gripping) traps can work, but must be placed in a spot where pets cannot get to them. They do pose a risk to other wildlife, as well as pets and people. An animal that steps into one does not get a second chance. Leg hold traps can be effective, but it is tricky to set them properly, they pose a risk to pets, wildlife, and possibly people. If you do use traps and need to move a dead raccoon, be careful to use rubber gloves.  Raccoons can harbor the nematode Baylisascaris procyonis (“raccoon roundworm”) that can parasitize people. Raccoons can be infected with rabies virus, which is lethal to people.

Other Carnivores

Opossum occasionally feeds on sweet corn, and some fruits (cantaloupe?). It is an omnivore that feeds on carrion, and also eats fruits & grains. It is more active at night than by day. Electric fencing is the most appropriate control method.

Red fox is common in New England, and sometimes feeds 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

USDA Wildlife Services staff are available to assist with a variety of wildlife damage issues, including voles. 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/

Bird Damage Prevention For Northern New England Fruit Growers https://extension.unh.edu/resources/files/Resource001797_Rep2514.pdf

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

Two local companies with experience and helpful information on fencing and bird netting options are Wellscroft and Orchard Equipment Supply Company.  Wellscroft Fence Systems is in Chesham, NH, and many fencing options are shown in their catalog online. www.wellscroft.com  1-855-327-6336.

OESCO is located in Conway, Massachusetts and has been very helpful to many orchardists in figuring out how to set up and what to order for bird netting.  Their website is at www.oescoinc.com  and telephone number is 1-800-634-5557.  They also have a detailed catalog online.

Carpe diem technologies www.carpediemtechnologies.com  offers laser bird scare devices.