Relative Effectiveness of Repellents for Preventing Deer Damage to Japanese Yews

Abstract

Homeowners whose landscape plants are repeatedly browsed by white-tailed deer (Odocoileus virginianus) are interested in repellent products that are effective and long-lasting. New products come to market with limited experimental testing. We conducted a 10-week trial from Feb. through Apr. 1999 to test the duration and efficacy of six commercial deer repellents [Deer-Away Big Game Repellent (BGR) mix, BGR spray, Deer-Off, Deer Stopper II, Repellex, Tree Guard] and two experimental deer repellents (CU-A and CU-B) relative to each other and to untreated plants. Treated and control balled japanese yew (Taxus cuspidata) shrubs were placed at each of 10 homeowner sites with known white-tailed deer damage near Ithaca, NY. Yews are frequently eaten by deer during winter and provide a good bioassay for testing repellents, especially during the winter months. We checked shrubs once weekly and took photographs of damaged yews to measure the amount of deer browsing. We calculated the surface area of shrubs in each photograph by using digital analysis software. To determine significant differences over time, we applied statistical analysis using analysis of variance. Deer repellents that provided the most consistent protection were BGR spray, BGR mix, Deer-Off, and Deer Stopper II. The japanese pachysandra (Pachysandra terminalis) extracts in experimental repellents CU-A and CU-B were not effective. The performance of other commercial repellents varied considerably among sites, and these products were unreliable.