Taking an environmentally sensitive approach to pest management


Missouri Environment & Garden



AUTHOR

David Trinklein
University of Missouri
Division of Plant Sciences
(573) 882-9631
trinkleind@missouri.edu

Critter Control in the Garden

David Trinklein
University of Missouri
(573) 882-9631
trinkleind@missouri.edu

Published: July 1, 2009

Pest control in the garden usually conjures up images of fighting a seasonlong battle with insects, diseases and weeds. As troublesome as the latter three might be the damage they inflict often pales in comparison with that caused by some of four-legged “friends”. It is extremely frustrating to put time, effort and money into establishing an attractive garden only to have it decimated by the likes of deer, rabbits and squirrels. An abundance of wildlife coupled with a shift in human population to more rural and suburban settings makes the control of wildlife in the garden more of a challenge today.

Wildlife biologists suggest that motivation and habituation are two important factors that dictate the likelihood of garden damage by wildlife and probability of their successful control. The more highly motivated wildlife is to feed the more difficult it will be to prevent damage to cultivated plants. Hunger is a tremendous stimulus. During periods of dry weather when food in the wild is sparse wildlife will be highly motivated to feed on garden plants. Additionally, once wildlife become accustom to using the garden as a food source it becomes more difficult to prevent future deprivation. Early intervention is important if control is to be successful.

Controlling wildlife damage is best accomplished using Integrated Pest Management (IPM) strategies starting (when possible) with planting resistant species. Plants that have pubescent or hispid leaves, pungent aromas or a bitter taste usually are shunned by wildlife. For example, the following table is a partial listing of popular ornamental plants that deer tend to shun because of texture, odor or taste.

Devices or techniques that frighten wildlife can be effective deterrents when used properly. Propane exploders and pyrotechnic devices such as noise bombs, screamer shells and firecrackers are examples of auditory repellants. The result (of their use) is not permanent and their effectiveness depends on the frequency of use as well as the ability of wildlife to become acclimated to the noise. Variables such as timing and diversity of noise also must be considered. For example, once in place, nuisance animals such as birds are less likely to respond to noise once they have habituated an area. Additionally, a variety of noises is more effective than a single noise used repeatedly.

Visual devices that frighten animals such as scare crows, predatory bird figures, tin foil or pie plates and mirrors can be helpful. As with noise, the tendency for wildlife to become acclimatized to these deterrents lessens their effectiveness. Relocating them on a regular basis is recommended.

Chemical wildlife repellents usually are classified as gustatory (taste) or olfactory (odor) in their action. These repellents most often are sprayed (brushed) on vegetation and may contain a sticker of some sort to make them more rain-fast. Their effectiveness depends on a number of factors including motivation of the animal to be repelled, habituation of the animal(s) in question, concentration of the repellent, palatability of the plant being protected, rainfall and number of applications. Suffice to say the hungrier an animal is the less likely it will be deterred by a chemical repellent.

An easy “home-made” repellent consists of a mixture of 20 percent whole eggs and 80 percent water (by volume). It reportedly is quite effective against deer. This mixture tends to withstand weather but should be reapplied on a monthly basis. Commercial repellants are widely available and vary with regard to active ingredients. Several newer products contain capsasin, the chemical that imparts the “fire” to hot peppers.

When choosing chemical repellents, factors such as human (or pet) safety, toxicity to plants, and expense should be considered.

Fencing, netting, cages or other methods that exclude wildlife from garden plants can be very effective in controlling damage. However, depending on their nature and the building material used, they can be expensive. The use of 36 inch high chicken wire buried six inches in the soil is effective in controlling small animals such as rabbits or squirrels. A fence eight feet in height is considered to be an effective barrier for deer and wildlife other than birds. Woven wire (chain link) fences are most effective; synthetic netting (mesh) can be used but represents less of a physical barrier to highly motivated animals. Placing small cages of wire or netting over individual plants to deter wildlife can reduce expense but detracts from the aesthetic value of a garden.

Electric fences represents somewhat of a compromise between initial expense and effectiveness in wildlife control. The number and spacing of fence wires depends on the species of wildlife to be controlled. For small animals such as rabbits, electrified wires located two and four inches above the soil surface should be sufficient. For deer, a series of three wires located 18, 36 and 54 inches above ground has proven to be effective. Baiting the fence by hanging strips of aluminum foal coated with peanut butter on the wires will help “educate” deer on the nature of electric fences and keep them from charging through them on first encounter. In all cases electric fences should be clearly labeled for safety purposes and monitored on a daily basis.

Table 1. Ornamental herbaceous plants considered to be deer resistant
AgeratumGaillardiaMarigoldSalvia
AsclepiasGeraniumMorning gloryShasta daisy
BarronwortHardy fernsNasturtiumSiberian squill
BergeniaHerbsNicotianaSnapdragon
Bleeding heartHelioropeOrnamental onionStatice
CannaHyacinthPansySunflower
CleomeJapanese anemonePetuniaSweet alyssum
Coral bellsJapanese spurgePhloxSweet William
ColumbineLamb’s earPlumbagoTickseed
DaffodilLamiumPoppyVerbena
DahliaLarkspurPurple coneflowerVinca
Dusty millerLavenderRanunculusYarrow
Foam flowerLiatrisRudbeckiaYucca
FoxgloveLily-of-the-valleyRussian sage 
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REVISED: October 26, 2012