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Vertebrates in the Vegetables

Perhaps nothing is as frustrating to a gardener as losing their hard work and crop to unwelcome wildlife. After working hard all spring to get plants and seeds into the ground, fighting the weather, and conquering the weeds, just when the harvest is to begin some other vertebrate critters begin to harvest the plants. Rabbits, ground squirrels, tree squirrels, pocket gophers, or deer arrive to take advantage of the plantings you have provided--assuming you provided food just for them!

The two major defenses gardeners have against such competition are: repellents and exclusion. Repellents are either area repellents or taste repellents. Area repellents repel the animal by smell. As the name implies, the chemical is aromatic and fills the air in the general area of the planting. The smell is offensive to the animal and it avoids the area. Examples of such repellents include hanging bags of human hair or bars of soap or commercial products like moth balls (naphthalene).

Taste repellents are more effective in that they are applied directly to the plant and repel the animal by having a bad taste. The idea is that the animal may sample the plant once, but the bad taste keeps it from trying it again. Examples include such "home remedies" as cayenne pepper and commercial products containing such chemicals as thiram, putrescent egg solids, or other foul-tasting products.

Repellents are not, however, a cure-all. Area repellents are limited in effectiveness, but may be useful if placed around the perimeter of the garden area. Taste repellents cannot be applied to plants you intend to eat since you would also find the taste offensive, and thus are mostly useful in landscaping. Most repellents must be reapplied regularly, especially after rain or periods of extreme heat. Not all products are registered for or effective against all species. And, if an animal is hungry enough, they will often ignore the bad smell or taste. Despite these limitations, many gardeners may find repellents to be the best alternative in their particular circumstance.

Another more permanent protection against unwanted sampling of your garden is exclusion. You may exclude in several ways, depending upon the area you are in and the situation. Individual plants may be surrounded by plastic tubes, chicken wire, or hardware cloth fences. You may also fence off your whole garden area to exclude the worst offenders – rabbits and deer.

The size and mesh of the fence depend upon what you are trying to exclude. For rabbits, 1-inch mesh "chicken-wire" fence at least 2 feet high will successfully exclude them, especially if the bottom 2-3 inches are buried below ground level. For deer, you may use a variety of fences including electrical tape or strong large mesh of any kind. Old "hog wire" fencing filling many farm gullies will suffice, especially if several sections are erected, reaching a height of 8 feet. In small garden plots, you may be successful with fences somewhat shorter than that, but no lower than 5-6 feet.

Gardeners may find also that general clean-up of garden areas to eliminate the brush, log, or junk piles that provide protective cover for many of the offending critters will help. Also, the presence of pet dogs will often serve as an aversion to these wildlife.

Above all, keep in mind that a reality of gardening is dealing with pests and factors out of your control like weather. Gardens inevitably attract both those critters you want and those you don't. Some damage should be expected. When your tolerance level for such damage cannot be raised any higher try some of these repellent or exclusion methods.

White-tailed Deer: Damage Management

With their large size, conspicuous habits, and distinctive tracks and scat, white-tailed deer are probably the easiest animals to pinpoint as a potential threat to plant growth. Indeed, you can often witness the actual offense taking place when the culprit is a deer. But unlike birds and small mammals, which tend to inflict most of their damage around the farmyard itself, deer pose a more widespread problem because they also feed on crops (particularly corn) and trees (such as in orchards) in the far reaches of the property.

Damage and losses caused by white-tailed deer in Iowa

  • Consume corn and soybeans in agricultural fields, causing economic losses.
  • Eat leaves and twigs of trees and shrubs in yards, orchards, and tree farms, sometimes causing permanent disfigurement or death of plants.
  • Enter yards and consume landscape and garden plants.
  • Eat stored feed intended for livestock.
  • Collide with automobiles on roadways, leading to vehicle damage and injury or death of motorists.
  • Stunt forest regeneration by over-browsing seedlings of oaks, hickories and other trees.

Identifying deer damage

Whether in a distant corn field or a row of fruit trees along your garden, deer damage can be directly identified by the jagged (uneven) marks they leave after tearing off the growing portions of plants. These signs differ considerably from the more sharply defined cuttings left by rabbits and some other small mammals, which have both upper and lower front teeth that enable them to cleanly snip vegetation. Deer can exploit just about any type of plant on your property but their greatest impact is more prominent along edges where they spend most of their time.

Deer, like all herbivores, prefer actively growing portions of plants, like shoots, buds, and sprouts. On growing corn, deer target the newest, greenest growth from when the corn is just a few inches tall all the way to the end of the growing season. They become even more determined when the corn reaches about 2.5 feet in height, which is a very comfortable eating height for both bucks and female deer. This habit of feeding higher on the plant helps distinguish deer from other animals that knock corn over or eat lower on the plant. Deer continue to target the newest shoots on the stems at this height, often leaving the horizontal leaves intact. Weeks later, the deer shift to pulling freshly emerged kernels from the cobs, which can in turn lead to obvious stunting and infection of the cob for the remainder of the season. When the corn becomes more fully developed, deer will chew off big chunks from healthy cobs that escaped earlier attacks. Although deer feed on different portions of the plant in different ways across the year, the damage remains distinctive and easy to separate from other cropland intruders, like raccoons or beavers.

Managing the negative impacts of white-tailed deer

Population control

White-tailed deer are a popular game species in Iowa, and consistent harvest of adult female deer can be an effective way to control their population and thus their impacts on farms and forests. Landowners can help maintain the balance of local deer populations by taking advantage of established seasons to allow hunters to legally harvest deer from their property. This is especially relevant for landowners who live in areas with high deer densities, like heavily forested areas or areas adjacent to refuges like cities. Special harvest seasons and tags are available to landowners who have high economic losses to deer that cannot be controlled through regular hunting seasons. Contact a Wildlife Depredation Biologist from the Iowa Department of Natural Resources for more information on those tags and other services this program provides to address deer damage.

Exclusion

The surest way to prevent deer damage issues is to exclude them from crops or landscapes where they may do harm. There are several options for keeping deer our of the areas where they cause damage.

Small-scale exclosures. In the farmyard or similar settings, an effective, targeted approach is to place woven-wire cylinders around young trees and shrubs (and around the trunks of larger trees) to prevent deer from browsing on the twigs and fruit or damaging the trunk with their antlers. This widely used, cost-effective method also helps to keep pesky rabbits off of these plants. Modern snow fencing, which is comparatively inexpensive and simple to install, can also be used in the same way to exclude deer and rabbits from single or multiple plants, such as clusters of shrubs or fruit trees.

example of protection against deer and rabbit damage
Wrapping young trees can protect them from deer as well as rabbits.

Deer exclusion with pallets and with snow fence
Sometimes creative solutions are needed to protect trees from deer, such as the pallet that protected the tree on the left and the drift fence protecting tree plantings on the right.

Fences. The most effective means of reducing deer damage on broader portions of your property is by constructing fences around vulnerable areas, such as crop fields, larger vegetable gardens, and orchards that span multiple acres. Fencing can be expensive and highly labor intensive, but will eliminate deer problems if constructed and maintained appropriately. The first line of defense selected by many landowners involves the installation of passive exclusion fencing that does not involve any sort of electrical charge as a deterrent. The design can vary somewhat depending on the terrain, but some tried-and-true specifications help to keep deer from going under, over, or through any openings. Regardless of the setting, a passive-exclusion fence must be at least 8 feet in height to prevent deer from leaping over them – and provide a barrier all the way to the ground to keep deer from ducking beneath. To accommodate these upper and lower barriers, you can install tall (16-foot) poles – anchored 4-6 feet into the ground – and space them at intervals of about 40 feet. String multiple strands of high-tensile wire or tall welded-wire fencing between the poles.

woven wire deer fence
Woven wire deer fence.

Active-exclusion fences use electricity to keep deer from entering. When deciding what type of active-exclusion fence to use, consider whether deer need to be excluded year round or just seasonally and how large the area of exclusion needs to be.

Temporary electric fencing can be less expensive and easier to install than permanent fences. Research has shown that products using synthetic rope or ribbon with conductive wires running through can be highly effective for reducing deer damage. These types of fences are generally only useful for areas smaller than 40 acres but they can be put up and taken down fairly easily if they are only needed at certain times of the year. Short electric fences can be effective in discouraging deer from entering small patches or gardens, but need to be tall or angled to prevent entry into larger (more than 100 square feet) patches. The number of strands necessary to deter deer can vary depending on how motivated the deer in the area were. Applying thinned peanut butter to synthetic fence at deer nose height can increase effectiveness, as deer will learn quickly that the fence is electrified.

small scale electric fence around sweetcorn patch
Short electric fences can be effective in discouraging deer from entering small areas like sweet corn patches and gardens. 

​​​Permanent electric fencing is more costly and can be labor intensive but methods for installing them are becoming less difficult. High-tensile electric fences seem to be the most effective permanent electric fencing option. Three different set-ups are often used: 5 foot vertical 5 strand, 5 foot 6-7 strand slanted, and 3.5 ft offset or double fence. Research has shown that the 5 foot vertical 5 strand fence is often most effective. 

Note: The effectiveness of any fence will vary greatly in different settings. Adjusting the height and number of strands on temporary fences can be useful based on the level of deer pressure in your area. Additionally, research has shown that removing a few deer that habitually get through a fence can often be effective.

five foot vertical fence diagram

A 5 strand electric fence with a hight of 5 feet is tall enough to discourage deer from trying to access an area. Diagram adapted from VerCauteren et al. 2006. Fences and Deer-Damage Management: A Review of Designs and Efficacy. Wildlife Society Bulletin 34(1). 

five foot slanted fence diagram

Building an electric fence that is both tall and wide like the slanted style is effective because deer cannot jump as high when they are also trying to clear a wide distance. Slanted fences can be built so they lift up to make mowing easier. Diagram adapted from VerCauteren et al. 2006. Fences and Deer-Damage Management: A Review of Designs and Efficacy. Wildlife Society Bulletin 34(1). 

offset fence diagram

The offset style electric fence is a shorter option that still prevents deer from accessing an area because it is too wide for the deer to jump across. Diagram adapted from VerCauteren et al. 2006. Fences and Deer-Damage Management: A Review of Designs and Efficacy. Wildlife Society Bulletin 34(1).  

Learn more

For more information check out the Iowa DNR Wildlife Damage Management page. There you can find an article on identifying crop damageabatement techniques to deal with damage, and information on options available to producers with deer damage. Nebraska also has a useful publication on deer damage management.


This article is an update of "Managing Iowa Wildlife: White-tailed deer" (PM-1302g) originally authored by Lynne Fischer, William Clark, and James Pease.