White tailed deer are notorious for destroying landscape trees, shrubs, bedding plants, and gardens either by feeding or antler rubbing. This can be incredibly costly to your landscape investment, as the damage often decreases aesthetic value and can be fatal when damage is extensive. For this reason, deer browse deterrents are utilized as part of overall plant health care.
In landscapes, most newly planted trees are susceptible to deer antler damage in the fall and early winter, but red maple, black cherry, willow, and pine are particularly commonly targeted and multi-stem magnolia appear to be the favorite. Damage caused by deer feeding is even less discriminate, but arborvitae and Leyland cypress are often stripped of their lower foliage and rarely fully recover from the damage. Rose, yew, rhododendron, and azalea are also highly susceptible to damage from feeding deer.
Fall/Winter Deer Management (Antler-Rub Damage)
Protection of susceptible plants from deer antler damage can be extremely difficult. Physical barriers such as metal or plastic trunk sleeves or wraps can help newly planted trees withstand the fall/winter risk period of antler rubbing, and soaps and odor deterrents can push deer to other, unprotected trees. At Burkholder Plant Health Care, we are experimenting with a new, inexpensive method to control deer antler damage on highly susceptible plants, and field trials will take place this fall.
Fall/Winter Deer Management (Feeding/Browse Damage)
With deer increasingly targeting residential landscape plants as winter food sources, the need for reliable protection of high-value and high-susceptibility plants has never been greater. For landscape plants, a vast majority of damage occurs as plants senesce and enter dormancy. As fall settles into the landscape, it is also happening in unmanaged plants as carbohydrate resources (fruits) decay and high-protein resources (mast crops such as acorns) are consumed, significantly reducing the overall food availability. Given heavy localized deer populations and limited wild food resources, deer naturally move to areas of greatest plant vigor and succulent growth…managed landscape plants.
In dormancy, there are two basic methods of protecting plants from deer feeding: area repellents and contact repellents. Area repellents are generally applied as a large boundary (property edges) or small boundary (bed edges) treatment, with the objective of keeping deer from entering the protected zone, while interior plants do not receive any direct protectant. This is the human equivalent of saying something like “nothing to see here.” Contact repellents are applied directly to plants that are prone to deer damage, and serve to change the taste/texture profile of the plants themselves, more like putting soy sauce in your coffee, where the plant looks the same as a food crop, but tastes or feels radically different, conditioning deer (which are highly prone to behavioral control) over time to avoid protected plants outright.
As a single component, area repellents may only reduce deer-browse damage by roughly 25%, while contact repellents reduce damage by as much as 75%. When applied properly, the combination of the two can synergize the effects to the point that deer will avoid protected properties completely.
Spring/Summer Deer Management
During the growing season of spring and summer, there are aspects of both plant biology and deer behavior that a) make overall behavioral control of deer easier and b) make control of deer feeding damage on certain preferred plant species more difficult. Spring and summer control of deer feeding on protected properties leans heavily on area repellents, pushing deer back into unmanaged areas where food is plentiful and acclimated movement into protected properties can be controlled.
Interestingly, most of these spring/summer approaches to deer management rely on deer’s natural aversion to predators, with materials applied at property or bed edges designed to release volatile odors that are reminiscent (to the deer) of predators. This can be accomplished by using
- pure predator urine in slow-release capsules (coyote, wolf, or mountain lion)
- other sulfur-producing applications such as putrescent egg solids or ammonia soaps/fatty acids
- volatile materials of human presence such as bone or blood meal, sachets of human hair, or by hanging bars of soap (most commonly recommended is Irish Spring)
Contact materials such as bittering agents or hot-pepper compounds can also be used in spring and summer to directly protect highly sought-after species such as hostas. However, the difficulty in use of contact deterrents in spring and summer is that these materials are only effective on plant tissues that are directly covered, and plants are actively, rapidly growing and expanding during the season, constantly generating unprotected plant tissue. As with fall/winter deer management, the best spring/summer strategies capitalize on the strengths of both systems (area repellents and contact repellents), and can reduce deer-browse damage by as much as 90%, even on plant species that deer consider as highly preferred.