How to Manage Pests
UC Pest Management Guidelines
Scientific Name: Odocoileus hemionus
(Reviewed 9/08, updated 9/08)
In this Guideline:
Description of the Pest
Mule deer, including the subspecies called black-tailed deer (O. hemionus columbianus), can be serious pests when trees are young. Deer occur in many foothill and coastal orchards and sometimes in the Central Valley near riparian habitats.
Young trees can be severely stunted, deformed, or killed when deer browse on new shoots. Bucks occasionally break limbs off of smaller trees or injure the bark when they use trees to rub the velvet off their antlers. Deer feeding on older trees seldom causes significant damage.
If deer are causing significant damage, deer-proof fencing provides the most effective and lasting control. Fencing also substantially reduces crop theft and vandalism. Fencing is costly, but if you are planting orchards where deer and uninvited people are likely to present continuing problems, it will likely pay for itself in the long run.
Deer feed mostly at night. To confirm their presence, look for tracks and fecal pellets in the vicinity of damaged trees. Deer hooves are split, pointed at the front and more rounded at the rear, and are about 2 to 3 inches long. The appearance of droppings varies, but commonly each fecal pellet is oblong, somewhat pointed at one or both ends, and 0.25 to 0.5 inch long. You may also use spotlights to check for deer at night.
Fencing is most effective for excluding deer when it is put in place before you plant the orchard. Fences must be at least 7 feet high in order to exclude deer. On sloping terrain, an 8-foot or taller fence may be necessary. Woven wire fences are used most often in California. Electric fences and mesh fences made of polypropylene are also used. Your choice of fence will be influenced by the potential severity and cost of deer damage, how long you expect to require protection, and the topography of the area. When encountering a fence, a deer will try to go under first, through second, and over last; keep these priorities in mind when building fences.
Woven Wire Fences
A fence made of woven wire exclude deer if the fence is tall enough. You can use a 6-foot (1.8 m) fence of woven wire with several strands of smooth or barbed wire along the top to extend the height to 7 or 8 feet. Be sure the fence is tight to the ground or deer will crawl under. Check the fence periodically to make sure it is in good repair and that no areas have washed out, allowing deer to crawl under the fence. Smaller-mesh fencing installed and properly buried along the bottom of the taller fence will exclude rabbits as well as deer.
Wire mesh cylinders around individual trees may be effective where only a few new trees are being planted in a location subject to deer damage. Make the cylinders at least 6 feet tall and large enough in diameter to keep deer from reaching over them to eat the foliage. Secure the cylinders with stakes so they cannot be tipped over.
Electric fencing is less expensive to install than woven mesh fencing but it costs more to maintain. High-tensile wire is the best choice, as it is more resilient than other types; it can absorb the impact of deer, falling limbs, and farm equipment without stretching or breaking. Use a high-voltage, low-impedance power source that provides sufficient voltage to repel deer while being less likely to short out when vegetation touches the wires. Control vegetation around the base of the fence; in wet weather, contact with wet foliage can drain enough voltage from the fence to render it ineffective.
Habitat management usually is not feasible for deer control because deer travel long distances to reach food. Repellents may offer some protection to tree foliage, at least for a short time, but they must be reapplied after rains or as new foliage emerges. Noisemaking devices may be effective for a few days, but deer will quickly grow accustomed to them.
If only a few deer are involved, having someone patrol newly planted orchards at night with a spotlight to frighten deer away may prove effective, though expensive. The California Department of Fish and Game can issue depredation permits to allow you to shoot deer when they are causing damage. This may be necessary if a deer gets inside a fenced orchard and is not able to escape. Shooting will not solve a serious deer problem; it may, however, prevent damage long enough to allow you to construct a fence.
UC IPM Pest Management Guidelines:
Acknowledgment for contributions to Vertebrates: