Identification | Biology | Damage ID | Management | Handling
Overview of Damage Prevention
and Control Methods
Habitat Modification
- Drain and grade waterways and levees
- Control vegetation
- Manipulate water levels
- Deep plowing to destroys dens
- Locate crops as far from waterways as possible
- Plant later in season
Exclusion
- Fences – 2-inch mesh, 4 feet tall with an apron buried at least 6 inches and extending 12 inches
- Single-strand electric wire 6 inches aboveground
- Xcluder™ Geo to protect embankments
- Rip rap or gabions on embankments
Frightening
- None are effective
Repellents
- None available
Toxicants
- Zinc phosphide-treated baits
Shooting
- Rifle- .22 caliber rimfire
- Shotgun– 12-gauge
Trapping
- Foothold traps – Nos. 1, 1.5, and 2
- Body-gripping traps – No. 220
- Cage traps- 10 x 12 x 32 inches or larger
- Cable-restraints – 3/32 with 7 x 7 strands
Other Control Methods
- Dip nets
Damage Prevention and Control Methods
Nutria are controlled best where they are causing damage and when they are most active. Control in sugarcane, for example, should be done during the growing season, after damage has started and when nutria are relatively sedentary and concentrated in drainages adjacent to fields. Conversely, efforts to protect levees in rice fields or the shorelines of southern lakes and ponds should be initiated during the winter when nutria are mobile and concentrated in major ditches and other large bodies of water.
Bait may be used to gather nutria in specific locations where they can be more easily controlled. After the main concentrations of nutria are removed, efforts should be directed at removing the remaining individuals. Preventive techniques should be used whenever possible, especially in areas where damage is prevalent. When control is warranted, all available techniques should be considered before a plan is implemented. The objective of control is to use only techniques that will stop or alleviate anticipated or ongoing damage, or reduce it to tolerable levels. In most cases, successful control will depend on integrating several different techniques and methods. Regulated commercial trapping should be an integral part of any management scheme because it can provide continuous, long-term income to trappers, maintain acceptable nutria densities, and reduce damage to tolerable levels.
Nutria have positive and negative economic attributes. They are economically important furbearers where their pelts provide income to commercial trappers. Conversely, they are considered pests when they damage property. The value of nutria must be compared with the cost of control when determining whether control is appropriate. Most people will not control nutria if the cost exceeds the value of the resource, or if control will adversely impact the income derived from trapping. The estimated value of sugarcane and rice damaged annually by nutria ranges from several thousand to over $1 million.
Habitat Modification
Land that is well-drained and free of dense, weedy vegetation generally is unattractive to nutria. Good farming practices such as precision land leveling and management of weeds can minimize damage by nutria in agricultural areas.
Drainages that hold water may be used by nutria. Eliminate standing water in drainages to reduce habitat for nutria. It may be difficult or impossible to drain or grade in low-lying areas near coastal marshes and permanent bodies of water. Higher sites, such as those used for growing sugarcane and other crops, are best suited for this type of management. On poorly-drained soils, contour small ditches to eliminate low spots and enhance rapid drainage. Use precision leveling on well-drained soils to eliminate small ditches that occasionally are used by nutria.
Grade and bulldoze areas to destroy active burrows in the banks of steep-sided ditches and waterways. Before grading and bulldozing, consider the potential impacts to other wildlife. Contour bank slopes at less than 45o (1:1) to discourage new burrowing; lower-angled slopes (2:1 or 3:1) are even more effective. Similarly, sculpt levees of rice fields to reduce the slopes.
Eliminate brush, trees, thickets, and weeds from fence lines. Remove row crops that are adjacent to ditches, drainages, waterways, and other wetlands to discourage nutria. Burn or remove vegetation from the site. Piles of brush that are left on the ground or in low spots are ideal summer habitat for nutria.
Many low-lying areas along the Gulf Coast are protected by flood-control levees and pumps that can be used to manipulate water levels. Decrease water levels in the summer to create stressful conditions that may cause nutria to concentrate in remaining aquatic habitat. Concentrations of nutria increase competition for food and space, exposure to predators, and emigration to other habitats. Increase water levels in winter to force nutria out of their burrows and expose them to the additional stresses of cold weather. Manipulation of water levels is expensive, and it may not be completely effective; nevertheless, it should be considered to enhance the effectiveness of other methods of control.
Continuous deep plowing of land can destroy shallow burrows and discourage new burrowing activity. Alternative sites for fields and gardens should be considered in areas where damage by nutria occurs on a regular basis. New fields, gardens, and slab-on-grade buildings should be located as far as possible from drainages, waterways, and other bodies of water where nutria live. Late-planted baldcypress seedlings are less susceptible to damage by nutria than those planted in the spring. Plant unprotected seedlings in the early fall when alternative sources of food are available readily.
Exclusion
Fences, walls, and other structures may reduce damage caused by nutria, but high costs usually limit their use. Barriers usually are too expensive to be used to control damage to agricultural crops. Low fences made of 2-inch mesh that are 4 feet tall with aprons buried at least 6 inches and extending 12 inches out are effective to exclude nutria from home gardens and lawns. Shields made from sheet metal can be used to prevent gnawing of wooden and Styrofoam® structures and trees, though sheet metal can be unsightly and expensive to erect. A single strand of electric wire positioned 6 inches aboveground has proven effective at excluding nutria. Use a UL®-approved fence charger and set the wire back from the edge of the water to reduce hazards from electric shock.
Xcluder™ Geo is a fabric impregnated with strands of stainless steel. It has been successful in preventing incursions by nutria into banks covered with the fabric.
Protect seedlings with hardware-cloth tubes around individual plants or wire-mesh fences around the perimeter of a stand. Plastic is not effective because nutria can chew through it.
Protect stream banks from nutria that are burrowing by installing sheet piling, bulkheads, gabions, and riprap. Installation requires heavy equipment and is expensive, limiting these techniques to industrial, commercial, or high-value applications.
Frightening Devices
Nutria avoid people, unless they are being fed, and will try to escape when threatened. Loud noises, high-pressure water spray, and other types of harassment have been used to deter nutria from lawns and golf courses. The success of frightening devices usually is short-lived and problem individuals soon return. Consequently, frightening as a stand-alone technique is neither practical nor effective.
Repellents
No chemical repellents are registered for the control of nutria.
Toxicants
Zinc phosphide is the only toxicant that is registered for controlling nutria. Zinc phosphide is a Restricted Use Pesticide that only can be purchased and applied by certified pesticide applicators or individuals under their direct supervision. It is a gray powder with a garlic smell that is widely used for controlling many species of rodents. Zinc phosphide is highly toxic to wildlife and humans, so read, understand, and follow all precautions and instructions on the label. When used properly, zinc phosphide poses little hazard to non-targets. Use a respirator and wear elbow-length rubber gloves when handling zinc phosphide concentrate to prevent accidental poisoning.
Mix and store bait treated with zinc phosphide in well-ventilated areas to reduce exposure to fumes and dust. When possible, mix zinc phosphide at field sites to avoid transporting treated bait. Never transport mixed bait or open containers of zinc phosphide in the interior of a vehicle. Store zinc phosphide in a dry place in its original, watertight container because moisture causes it to deteriorate. Immediately wash off any zinc phosphide that gets on the skin.
The best places to bait nutria are in waterways, ponds, and ditches where permanent standing water and recent sign of nutria are found. The use of bait in these areas increases efficiency and reduces the likelihood that non-target animals will be affected. Small chunks of unpeeled carrots, sweet potatoes, watermelon rind, and apples are effective baits.
Observe sites with the prebait to determine how the program should proceed. If non-target animals feed at the sites (as determined by sign or observations of animals), prebaiting should start over at another location. Prepare and apply zinc phosphide-treated baits when nutria become regular users of stations with bait.
The act of prebaiting is crucial when using zinc phosphide because it leads to nutria feeding at specific sites on specific types of foods that are similar to the bait. Nutria tend to be communal feeders; if an individual finds a new feeding spot, other nutria in the area also will feed there. The act of prebaiting also may allow for the identification and avoidance of non-targets.
To prebait, lightly coat small (approximately 2 inches long) chunks of untreated bait with corn oil. Place the bait at each baiting station in late afternoon and leave it overnight. At any given time, use no more than 10 pounds of bait per raft, 4 pieces of bait per baiting board, or 5 pieces at other sites. Prebait should remain for at least 2 consecutive nights after nutria begin feeding at a site. Gaps of more than 1 week in the prebaiting sequence necessitates that the process be restarted.
The best bait stations for large waterways are floating rafts spaced ¼ to ½ mile apart throughout the damaged area. In ponds, use 1 raft per 3 acres. Rafts measuring 4 square feet or 4 x 8 feet are easily made from sheets of 3/8– to 3/4-inch exterior plywood and 3-inch Styrofoam® flotation devices. Install a thin wooden strip around the perimeter of the surface of the raft to keep bait from rolling into the water. The raft should float 1 to 4 inches above the surface and should be anchored to the bottom with a heavy weight or tied to the shore.
In small ditches or areas where densities of nutria are low, use 6-inch-square, floating bait boards made of wood and Styrofoam®. They should be held in place with a long, slender anchoring pole made of bamboo, reed, or other strong material placed through a hole in the center of the platform. Anchors allow the board to move vertically as water levels change. Attach bait to small nails driven into the surface of the platform. Bait boards should be spaced 50 to 100 feet apart where nutria are active.
Other sites surrounded by water can be baited for nutria, including small islands, tree stumps, floating logs, and feeding platforms. To avoid non-target losses, do not place baits on or near muskrat houses or beaver lodges. Bait can be attached to trees, stumps, and other structures with small nails and should be kept out of the water.
Place bait on the ground only when sites in water are unsuitable or lacking. Ground-baiting is justified and effective to eliminate nutria remaining in a local population. Bait on the ground may be accessible to non-targets. Place ground-baits near trails, entrances to burrows, and other activity sites of nutria.
Prepare zinc phosphide baits as needed to prevent deterioration. Baits are prepared in 10-pound batches, enough to treat 1 raft by using 10 pounds of bait (carrots or sweet potatoes are preferred), prepared as for prebaiting. Carefully follow the directions on the label of the pesticide.
To prepare treated bait, add corn oil to the bait in a 5-gallon plastic or metal container. Stir the mixture until the bait is lightly coated with corn oil. Sprinkle zinc phosphide over the mixture and stir until the bait is uniformly coated. Treated bait has a shiny black appearance and should be dried for about an hour in a well-ventilated area until the color fades to a dull gray. Baits that are dried properly are weather-resistant. Although bait that has been treated persists after light rain, it should not be used when heavy rain is expected or on open water with large or frequent waves.
The amount of untreated bait eaten the last night of prebaiting determines how much treated bait should be used on the first night of treatment. When all or most of the untreated prebait is gone from baiting stations by morning, the same amount of treated bait should be used on the stations the following night (e.g., up to 10 pounds per raft, 4 pieces per baiting board, and 2 to 5 pieces at other sites). When smaller quantities are eaten, reduce the amount of treated bait that is used per station proportionately. When only a few pieces of prebait on a raft are eaten, the raft should be removed and replaced with several scattered baiting boards.
The quantity of treated bait consumed each night is the quantity that should be put out the following afternoon. Continue baiting until no more bait is taken. Most nutria are controlled after 4 nights of baiting. When densities are high, control may require more time.
Carcasses of nutria killed with zinc phosphide should be collected as soon as possible and disposed of by deep burial or burning. Usually, only 25% of poisoned nutria die where they can be found by humans. Many nutria die in dens, vegetation, or other inaccessible areas. Fortunately, no true secondary poisoning occurs with zinc phosphide because the toxicant dissociates in the target animal to inert ingredients. Dispose of leftover bait that has been treated in accordance with the directions on the label. Cessation of damage is the best indication that zinc phosphide is controlling the problem.
Shooting
Shooting of nutria is most effective when done at night with a spotlight or red lens. However, night-shooting is illegal in many states and should not be attempted until proper permits have been obtained.
Nutria can be shot from the shoreline or from boats. Up to 80% of the nutria in an area may be removed by shooting with a shotgun (12-gauge) or small caliber rifle, such as the .22 rimfire. Take care when shooting over open water to prevent bullets from ricocheting.
Bait can attract large numbers of nutria to floating rafts, baiting boards, and other areas where they can be shot. Shoot from dusk until about 10:00 pm for 3 consecutive nights for effective control once a regular pattern of feeding has been established. Sites should be continuously lit by a spotlight and easily visible to the shooter from a vehicle or other stationary blind. At night, nutria can be located by red-shining eyes and a V-shaped wake left by swimming. Four to 5 nutria per hour can be taken by shooting at night. Shooters should wait 2 to 3 weeks before shooting nutria at the same site again.
Shoot nutria in the late afternoon or early evening from a small boat paddled slowly along waterways, large ditches, or the shores of small lakes and ponds. Nutria are especially vulnerable to this method when water levels are extremely high or low and when vegetative cover is scarce. At times, animals can be stimulated to vocalize or decoyed to a boat or blind by making a call that imitates the nutria’s nocturnal feeding and assembly call. This call can be learned from someone who knows it or by listening to nutria vocalizations at night. Limit shooting to no more than 3 nights, followed by 2 to 3 weeks of no shooting activity.
Nutria can be shot by slowly stalking along the banks of ditches and levees, a method which can be effective where nutria have not previously been harassed. Unlike night-shooting from a boat or blind, bank-shooting is most effective at twilight in the evening and morning. Several nutria usually can be shot the first night, though success decreases with each consecutive night of shooting. Daytime shooting from the bank of a waterway is effective in some situations.
Trapping
Damage to crops, levees, wetlands, and other resources may be minimal in areas where nutria are harvested by commercial trappers. The commercial harvest of nutria on private and public lands should be encouraged as part of a program designed to manage damage caused by nutria. Landowners can obtain additional information on management and trapping of nutria, as well as a list of licensed trappers in their area from their state wildlife agency or trappers association.
Foothold Traps
Foothold traps are the most common traps for catching nutria. Double long-spring traps, Nos. 1 or 2, are preferred by most trappers, however, the No. 1½ coil-spring, No. 3 double long-spring, and the soft-catch fox trap also can be effective. Foothold traps are more efficient and versatile than body-gripping traps and are highly recommended. Foothold traps should be used with care to prevent injury to children and pets.
Set traps just under the water where a trail enters a ditch, canal, or other body of water. Make trail sets by placing a trap offset from the center line of the trail so that nutria are caught by the foot. Traps can be covered with leaves or other debris, but nutria are captured easily in traps that are not concealed.
Bait can be used to lure nutria to foothold sets. Bait should be placed beside, rather than inside, the jaws of the trap. Foothold traps also are effective when set on floating rafts that have been prebaited. Use drowning sets when water over 3 feet deep is available. If deep water is not available, stake foothold traps to the ground or anchor them to solid objects.
Body-gripping Traps
A Conibear® No. 220 is the most common type of body-gripping trap used for controlling nutria. Place sets in trails, at entrances to dens, in culverts, and in narrow waterways. Body-gripping traps can be hazardous and should be handled with extreme caution. They should not be set in areas that are frequented by non-targets.
Cage Traps
Nutria are captured easily in cage traps that measure 10 x 12 x 32 inches or larger. Use cage traps when foothold and body-gripping traps cannot be set, or when captures of non-targets are likely. Bait cage traps with sweet potatoes or carrots and place them wherever nutria or signs of nutria are seen. A short line of bait that leads to the entrance of a cage trap will increase success of trapping. Cage traps placed on floating rafts will catch nutria, but prebaiting is necessary. A large raft can hold up to 8 traps. Nutria that are not wanted should be humanely euthanized. Non-target animals should be released.
Cable-restraints
Cable-restraints are effective in catching nutria and are relatively easy to set after appropriate training, safer than foothold and body-gripping traps, and almost invisible to the casual observer. Restraints constructed with 3/32-inch diameter, flexible (7- x 7-inch winding) stainless steel or galvanized aircraft cable are suitable for catching nutria. The loop should be 6 inches in diameter with the bottom 2 inches off the ground. Ready-made cable-restraints and components (cable, 1-way cable locks, swivels, and cable stops) for constructing cable-restraints can be purchased from trap suppliers. Consider using deer stops and break-aways for cable-restraints. Place cable-restraints in trails, other travel routes, feeding lanes, and bank slides. Check cable-restraints frequently because they often are knocked down by nutria and other animals. Check regulations, as cable-restraints are not legal in all states.
Other Control Methods
Nutria occasionally may be captured using a long-handled dip net. The handle can be 8 feet in length or greater but longer lengths tend to be difficult to move quickly with precision. Dip nets should be 20 inches in diameter and 20 inches in depth. Mesh size can be 1.5 inches for nutria 5.5 pounds or greater. Take care to avoid being bitten or scratched.
Alligators are not effective in controlling nutria.
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