Combat Wildlife Damage with Common Sense Control Methods
By: Dr. James L. Byford
Extension Wildlife Professor
University of Tennessee, Knoxville
It's tough to make a living these days if you work the land. And no matter how good you are at your business, there are some things beyond your control. The economy, customer whims and fads, and the weather - all are critical to your profit margin but beyond your control. Wildlife damage may seem that way, too, but you often have more control over this problem than you think.
Don't get me wrong: I didn't say it was easy. But if you think through your problem and put forth some effort, you can cut your losses maybe even eliminate them.
Think Through the Problem
People with problems caused by critters often ask the question:
"Is there something I can spray to get rid of the pest"? There may be some cases where a spray is feasible. But often there is an easier, more sensible way to solve the problem.
Wildlife damage control is the opposite of wildlife management. To manage wildlife, you must make sure that the animals have sufficient food, water and cover year-round. If you have unwanted wild animals around your nursery, it is a sure bet that there is already enough food, water and cover for them. The solution is to remove at least one of these elements - and if you can remove two, it's better.
In thinking through a wildlife damage problem, try a sequence something like this:
First - is there some way you can keep the animals from getting to the problem site? This may involve using hardware cloth (not screen wire - it's too weak), sheet metal or, in the case of holes in masonry, mortar.
If you can't build them out, can you repel them from the problem site? Sometimes you can use chemical repellents, visual repellents or even sound repellents to keep animals away from a problem area. One effective and inexpensive repellent system is electric fencing.
If you can't put up an effective barrier or repel the animals from the problem site, the last step is to remove the animals that are causing your problems. Trap the animals live and transport them to another site, shoot them, gas the dens or use poison baits.
However, when considering these alternatives, you should check with your county wildlife officer to get approval - unless the animals are unprotected. The house mouse, Norway rat, roof rat, domestic pigeon, English sparrow and starling are unprotected in most states.
In most cases, county wildlife officers will allow you to solve your problems. Sometimes they will even help you.
No entire species of wild animal is a pest all the time. Admittedly, some species are pests more often than not. The trick is to deal only with the animal or animals that are causing damage, not eradicate the species. You couldn't do that anyway.
A final consideration: Is it worth the effort? It often takes quite a bit of time and money to control a wildlife damage problem. If the economic loss is greater than the control cost, it's worthwhile to tackle a control program.
Let's take a look at some common pest species around the nursery and steps for controlling them.
Deer probably cause nursery managers more headaches than any other wildlife species. Browsing on tender new leaves and twigs is the most common problem. But deer can also cause expensive damage in early fall by rubbing their antlers against woody plants and removing the bark.
Fences are one common control method. The only way to insure 100 percent control of deer damage in a nursery is to build a low-impedence electric fence. This fencing system is not cost-prohibitive, especially for someone with as much invested as a nurseryman. Before a fence can work, though, it must be built properly. This type of fence is not temporary but permanent, and it should last at least 35 to 40 years.
There are several designs for this kind of fence, but the five-strand deer fence appears to be the most cost-effective. This fence uses five smooth, 12-gauge, high-tensile wires and a low-impedence charger. It's important to use this type of charger. It's expensive (about $250.), but it's the heart of the system and will charge 50 miles of fence.
I built a similar fence to keep dogs out of my sheep, and it was 100 percent effective. I even had on occasion to watch a deer's run-in with the fence. The little buck never came back!
The five wires in a high-tensile, low-impedence deer fence should be stretched to 250 pounds (112.5 kilograms) tension. The bottom wire should be 10 inches above the ground, and the other four wires should be 12 inches apart. If you decide to use this kind of fence, you can get more advice from your county extension agent or a company that sells the materials.
If you want a less-expensive temporary system, you may be interested in the peanut butter fence. Researchers in Minnesota and New York recently developed a simple, cost-effective, single-strand electric fence that repels deer by shocking them after they sniff an electrically charged bait wrapper. Of the deer observed, 82 percent were satisfactorily repelled in one study and 80 percent in another study. Deer that weren't repelled saw the fence first and either jumped it or crawled under it.
The fence design is simple. It involves one smooth wire three feet off the ground, with flags at 15-foot intervals. These flags consist of 12-inch strips of athletic tape placed across the wire and taped together, leaving a total length of six inches. Before taping, a teaspoon of peanut butter is sandwiched between the two halves of the strip.
A 6-by-12 inch piece of aluminum foil is then folded on the outside of the tape, so that the flag becomes a 6-by-6 inch piece of aluminum foil. As deer approach the fence, they sniff the peanut butter inside, touch the aluminum foil and receive a shock.
Common Deer Repellents
Repellents are another method of deer control. Nurserymen have used a number of deer repellents to control damage on small trees and shrubs over the years. Basically, there are two types: contact and area. Contact repellents are applied directly to the plants and repel by taste. New growth that appears after treatment is unprotected. Area repellents are applied near the plants and repel deer by smell alone.
Researchers in Connecticut recently tested the effectiveness of six common deer repellents on trees and shrubs:
- Human hair, collected from local barber shops and placed in nylon mesh bags, using two to four handfuls per bag.
- Magic Circle Deer Repellent (produced from bone tar oil), soaked into burlap strips measuring approximately 10 by 30 centimetres.
- Big Game Repellent, also known as Deer Away, made from putrescent whole egg solids.
- Hinder, made from ammonium soaps of higher fatty acids - diluted one part Hinder to seven parts water.
- Miller Hot Sauce, containing capsaicin, an extract of hot peppers - diluted one part Miller Hot Sauce to six parts Miller Vapor Gard and 1,600 parts water.
The Connecticut researchers used all repellents according to label instructions. Here's what they found:
- Hair was 34 percent effective. Damage between treated plots and untreated plots was significantly reduced in two of seven tests.
- Magic Circle was 18 percent effective. Damage was significantly reduced in three of seven tests.
- Big Game Repellent (Deer Away) was 46 percent effective. Damage was significantly reduced in three of six tests.
- Hinder was 43 percent effective. Damage was significantly reduced in both of two tests.
- Miller Hot Sauce was 15 percent effective. Damage was significantly reduced in one of four tests.
- Thiram was 43 percent effective. Damage was significantly reduced in two of five tests.
All of the repellents studied were only partially successful, but almost every one reduced deer damage to some extent. The cost per hectare (2.47 acres) was perhaps the most important factor: $24 for hair, $74 for Magic Circle, $990 for Big Game Repellent, $75 for Hinder, $26 for Miller Hot Sauce and $555 for Thiram. Labor was not included in any of these costs.
The researchers found that, under heavy browsing pressure, these repellents were not very successful. However, the tests were done on Japanese yew (Taxus cuspidata), which happens to be a highly preferred deer food. The researchers suggested that the repellents may be much more effective on a less-preferred plant species.
Other repellents used over the years include bone tar oil, mothballs or flakes (para-Dichlorobenzene), blood meal, Chaperone-soaked jute rope, tankage, bars of soap hung in trees, Z.I.P. (or ZAC) and cat feces. All of these have produced results at one time or another, but success is variable.
During the dormant season, apply contact repellents on a dry day when temperatures are above freezing. Treat young trees completely. It will be cheaper to treat only the terminal growth of older trees. Be sure to treat to a height of six feet above maximum expected snow depth.
If you use contact repellents during the growing season, apply at about half the concentration recommended for winter use to save money. Remember that success with repellents is measured by the amount of damage reduced, not by the elimination of damage.
Repellents' effectiveness depends on the weather and how hungry deer are. Some repellents must be reapplied after a rain. Others don't weather well, even in the absence of rain.
The availability of other, more tasty food will also have an effect on success. In some cases, it may be worth your while to provide deer with an alternative food source in conjunction with using repellents. For example, planting a strip of winter wheat for deer may pay. Some nurserymen have tried spraying mixtures of water,salt, and molasses or saccharine onto foliage adjacent to the nursery to make it sweeter than the nursery plants.
Don't worry that these methods will attract additional deer. Deer spend their entire lives in a relatively small home range, and they won't leave to come to new food sources.
Rabbits are valuable from a recreation and food standpoint, but they can cause severe nursery damage. Rabbit damage is often confused with deer damage, but on close examination, the difference is evident. Rabbits bite into shrubs at a smooth 45 degree angle; deer have no upper incisors, and their bite is ragged.
There are several methods of rabbit damage control:
- Habitat control. Because rabbits are heavily preyed upon, they can't live without abundant cover. Removal of rabbit cover is effective where damage is severe and economic loss is substantial. You should remove natural vegetation along ditches, fences, roads and odd areas as well as brush piles. Unfortunately, removing such areas may increase soil erosion and reduce the habitat of pollinators and pest predators as well as rabbits.
- Traps. Live traps can be effective in winter. Bait new traps with apples or carrots or even rabbit feces. Traps that have caught rabbits before don't need bait.
- Tree guards. Tree guards are made from 1/2 inch hardware cloth, light metal, or heavy plastic bands. If they extend at least two feet above the maximum snow depth, they effectively prevent rabbits from girdling bark. Tree guards may have limited usefulness in nurseries in terms of cost and labor effectiveness.
- Fences. Three-foot-high chicken wire fences are almost completely effective in excluding rabbits. The fence should be supported with stout wooden stakes or metal posts, and the lower edge must be tied to the ground to prevent rabbits from going under it. Rabbits will not dig under a fence, but they will squeeze through existing holes. So you should fill openings with soil or rock. The initial cost of such a fence is about 40 cents per linear foot. The fence should last from five to 10 years. You can build electric fences much more cheaply; use three strands of fine wire placed four, eight and 12 inches above the ground.
- Repellents. Several repellents discourage rabbits. You can apply some with a sprayer after diluting them with water or alcohol. Others can be mixed with a latex-based paint and applied with a paintbrush. Many commercial repellents contain the fungicide thiram and are available in a ready-to-use form.
Most rabbit repellents are taste repellents that make treated plant parts distasteful. New growth that appears after treatment is not protected. In addition, rain washes some repellents off and reapplication is necessary. Blood meal and mothballs are examples of odor repellents, but they have limited use in nurseries. Blood meal is unsuitable for bark application, and mothballs work only in closed areas.
Other rabbit repellents include ziram, tobacco dust and tree rosin. Tree rosin should be mixed at seven pounds per gallon of denatured alcohol. Allow this mixture to stand in a warm place for 24 hours, then paint or spray it on dry trees in fall. For large numbers of small trees, use a backpack sprayer; one gallon will protect 200 to 300 two or three-year old trees.
If your trees are suffering from girdled bark, the damage is probably caused by beavers, muskrats, rabbits or voles. Beavers will girdle some trees and completely cut through others. Since beavers and muskrats seldom cause this kind of damage in nurseries, I will not cover control of these species here. And we have already discussed the control of rabbits, which girdle higher on the tree than voles do.
This leave voles. Voles are sometimes called mice, but they are a specialized group of mice with short ears and tails. Voles should not be confused with shrews and moles, which do not eat bark at all. As a matter of fact, shrews are effective vole predators. Unlike voles, both shrews and moles have long snouts and no visible ears. In addition, moles have large, paddle like front feet.
There are several species of voles in the US, but meadow voles, prairie voles and pine voles cause the most nursery damage. If the damage is aboveground, it is probably caused by meadow voles or prairie voles. If problems appear belowground, pine voles are probably the culprits. Remember that damage several inches aboveground can be caused by meadow or prairie voles during snow.
Vole damage is best controlled in nurseries by a combination of cultural practices and poison baits. You should use herbicides to kill vegetation under the drip line of trees. Remove the dead vegetation that results. If you do not, the voles will continue to use this for cover while feeding on the only remaining food supply - the tree roots.
Avoid mulching this zone as well. The object is to keep the animals away from the tree roots and trunk by making the habitat unsuitable. You should keep vegetation between rows mowed as close to the ground as possible.
Cleaning fence rows and other vegetative borders around the nursery has some of the same effects for vole control as it does for rabbits. The home ranges of voles are smaller, but their populations are so explosive that natural cover often provides refuge for seed populations. Even if a control program is effective,these seed populations can quickly re-populate a nursery.
Tree guards made from rolled roofing, sheet metal or 1/4 inch galvanized hardware cloth can be used to combat meadow or prairie vole damage. However, this is not usually practical in a nursery situation: it is expensive and labor-intensive and also blocks access to the plants.
If used in combination with cultural practices, poison baits can be effective in knocking the vole population back to a tolerable level. There are two groups of poisons. One consists of single-dose rodenticides, which kill an animal after one feeding. Zinc phosphide is the most often used single-dose poison. The other group comprises the anticoagulants such as diphacinone (Ramik-Brown) and chlorophacinone (RoZol).
Anticoagulants won't kill animals after one feeding. Therefore, you need to make a plentiful supply available for at least two to three weeks. The advantages of anticoagulats are that they are safer around non-target species (including people) and that bait shyness will not develop because the animals never associate their weakened condition with the bait. Occasionally this happens with single-dose poisons.
Poisons can be mixed with baits, such as apple cubes or grain. Or you can opt for commercial poison-bait mixtures. Even though the latter are more expensive, they may be more practical because of labor costs involved in mixing - and the fact that such mixtures have been specifically formulated to attract voles.
Before baiting, it's always a good idea to prebait the area, setting out bait without poison for a few days before using the poison. Poison baits may be put out by hand or machine. Hand-placed baits can be broadcast directly under trees or, in the case of pine voles, can be placed under roof shingles or sawmill slabs. These items are placed under the trees two to three weeks ahead of time to concentrate vole activity.
Watch the weather report, and try to bait when vegetation is dry and the forecast calls for continued fair weather for at least two days.
Rats and Mice
Successful rat and mouse control involves two steps:
- Killing rats and mice that are already present.
- Removing the conditions that attracted the pests.
The most important step is to destroy hiding places and eliminate food and water. Rats like to find shelter in refuse and lumber piles. They like to burrow under floors and to nest inside double walls and attics.
Rats get their food from garbage cans, feed bins, granaries, corn cribs and other food storage facilities that are not rodent-proof. They also commonly feed on dog and cat food left after pets have finished eating. Rats get water from streams, ponds, stock watering tanks, ditches and even puddles of surface water around homesteads, farms and nurseries.
Anything you can do to create a less favourable environment for rats and mice will aid in their control. For example, if food, shelter and water are available in one building, rats are more attracted than if they must travel 100 yards from their shelter to find food and another 100 yards to get water.
For rat and mouse prevention, protect susceptible areas with 1/4 inch mesh hardware cloth or sheet metal. Store food in metal containers or use some other method to make it unavailable. If feasible, remove the water source.
You can kill rats and mice with either traps or poisons. Poisons are readily available and can be safe and effective if you follow directions. As with vole poisons, there are basically two types of rat and mouse poisons; single-dose and anticoagulants. Anticoagulants are generally preferred for rats and mice because of their relative safety around pets and children.
There are several anticoagulant poisons on the market, including some common ones like warfarin. Fumarin, Pival, diphacinone and chlorophacinone. Commercial preparations of bait-poison mixtures are available at feed, seed and hardware stores. Pure poison is also available for home mixing.
Anticoagulant poisons must be provided in plentiful supply for at least two to three weeks to be effective.
Moles have high energy requirements and actively feed day and night at all times of the year. Members of the order Insectivora, they feed on insects (mature and larvae), snails, spiders, small vertebrates, earthworms and small amounts of vegetation. Moles eat amounts equal to 70 to 100 percent of their weight each day and thus need access to large amounts of food.
Moles prefer moist, loose, sandy loam soils, which are easy to dig. They generally avoid heavy, dry, clay soils. They make extensive runway systems in a surprisingly short time, completing as much as 225 feet of tunnel in one day in suitable soil.
There are two types of tunnels formed by moles: those near the surface and those farther underground. Surface tunnels show up as ridges of upheaved soil, created as the animals forage for food. Some of these are used as travel lanes, others are travelled infrequently, and still others may be abandoned immediately after being dug. Surface tunnels are temporary and most abundant in spring and fall, especially after rains.
In summer and winter, burrows are deeper. The only evidence of these burrows is mounds of soil (molehills) pushed up to the surface as moles dig deep, permanent tunnels and nest cavities. These deeper runs are highways leading from a mole's home to its hunting ground. They are used especially during hot and dry or very cold weather conditions, when earthworms move deeper in the soil.
Because of their food requirements, moles must cover a larger area than most underground animals. The home range of a male eastern mole is thought to be almost 20 times that of some common rodent species. In addition, the eastern mole is considered a loner. Three to five eastern moles per acre is a high population; two or three per acre is more common.
Before starting a mole control program, be sure that moles are actually responsible for your problem. Moles normally do not eat seeds, bulbs or tree roots, although they are often blamed for it. If moles make runways in your nursery, it's because they are looking for insects and earthworms to eat.
The real culprits responsible for eating seeds and roots are mainly voles, white-footed mice and common house mice. These seed and plant eaters often live in mole runways, helping themselves to grains, seeds, bark and tubers. Yet moles get blamed for the damage.
The mole plays an important role in the management of soil and control of grubs. One of the most abundant small mammals, the mole has for ages been working the soil and subsoil. Only part of its work is visible at the surface. Tunnelling and shifting of soil particles permits better aeration of the topsoil and subsoil. This carries humus farther down and brings the subsoil nearer the surface where nutrients may be more available to plant roots.
If you still want to control moles after considering these facts, trapping is the only effective way. Trapping is successful only if care is taken in selecting the trap site. Remember that surface runways are made primarily for finding food. Many are not used more than once, while others serve as highways and are used regularly. Ordinarily, a runway that is more or less straight, or that seems to connect two systems of activity, will be in constant use.
Another way to determine which runways are active is to stamp down a short section (a shoe's width) of each runway with your foot. Observe the runways daily for several days, and restamp any raised sections. If a tunnel is raised daily, it is an active runway, and you should set a trap at this location.
There are three excellent types of mole traps on the market. These all depend on the same sort of mechanism for releasing the spring. A broad trigger pan triggers the trap as the mole pushes up the depressed portion of his burrow over which the trap is set. The brand names of these traps are
The Victor trap (harpoon-type) has sharp spikes that impale the mole when driven into the ground by the spring. The Out O'Sight trap has scissorlike jaws that close firmly across the runway, one pair on either side of the trigger pan. The Nash trap has a choker loop that tightens around the mole's body.
Woodchucks, commonly called groundhogs, cause no harm at all in many cases. But they sometimes forage on nursery crops and dig dens that pose a menace to machinery.
Groundhogs hibernate in burrows during winter. They may begin activity in March but don't usually become very active until warm weather sets in and the young are born. The young are born in spring, usually during April or May.
Groundhogs usually have two or three separate homes, which may be several hundred feet apart. Each den generally has two or more openings. The entrance hole normally has a large pile of freshly removed earth in front of it, and the exit hole, or plunge hole, will have no earth removed from it.
One common way to control groundhog damage is to gas the animals in their dens. Gas cartridges can be bought from farm supply stores. Control is usually more effective during early spring, since active burrows are easy to find and young groundhogs have not scattered.
Gas treatments should be applied during the hot part of the day, when groundhogs are least active. Most are in their dens at this time.
Here's how to do it:
- With a spade, cut a clump of grass sod slightly larger than the burrow opening. Dig one clump of sod to fill each burrow opening. Seal all openings except the one you put the cartridge in. Follow directions on the cartridge for the exact procedure for lighting it.
- Kneel at the burrow opening, light the fuse, and immediately place the cartridge as far down the hole as you can. Do not throw it; it will not explode.
- Immediately close the entrance by placing the sod, grass side down, over the opening to make a tight seal. Placing sod with grass side down prevents smothering the cartridge with loose soil. Stand by for three or four minutes and watch nearby holes, re-plugging those from which smoke escapes.
An electric fence is another effective method for groundhog control, if you use three strands of small wire at four, eight and 12 inches above the ground. In some cases, a single wire placed four inches high has been effective. Spray vegetation under the wires with herbicide to prevent sapping of the current through grounding.
In addition, three kinds of traps are available for groundhogs.
Live traps are effective if baited with apples or vegetables such as carrots and lettuce and placed near an active burrow. No. 2 steel (toe-hold) traps can be used if placed in the groundhog's path. You can use guide logs to funnel the animal to the trap. Conibear 330 traps are effective when placed in an animal's path or over the entrance of an active burrow. Conibear-type traps kill animals as they try to pass through.
All traps should be checked twice daily so that you can deal with the animals in a humane manner.
Remember, think through your problem before attempting control. What is the easiest, cheapest, most practical way to control the problem? What will be the least hazardous to pets, people and non-target wildlife? Are you losing enough money to justify control expense? Finally, remember that your goal is to reduce damage to a level you can live with. You can't wipe the critters off the face of the earth even if you want to.
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