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Home HortTechnology Preventing Deer Damage to Japanese Yews
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ITHACA, NY—Homeowners across the United States know all too well the destruction that deer can cause to yards and landscapes. In the U.S., the economic impacts attributed to deer damage have been estimated at a whopping $100 million annually in New York and Pennsylvania alone. Property owners are increasingly interested in effective and long-lasting deer repellents as non-lethal alternatives to thwarting deer damage to valuable landscape plants and trees. In a study published in HortTechnology, Cornell researchers tested the duration and efficacy of eight deer repellents and offered recommendations for landowners.

Non-lethal approaches to addressing deer damage—including fences, repellents, and scare devices—can be effective, but while fences provide the best protection against deer browsing, high construction and maintenance costs and poor aesthetics limit their applicability. To investigate whether deer repellents can offer economical, effective protection from expensive deer damage, Paul Curtis and Jason Boulanger conducted a 10-week trial using six commercial repellents (Deer-Away Big Game Repellent mix, Big Game Repellent spray, Deer-Off, Deer Stopper II, Repellex, and Tree Guard), and two experimental repellents they called CU-A (Japanese pachysandra extract) and CU-B (Japanese pachysandra extract mixed with synthetic fermented egg).

Balled-and-burlapped Japanese yew shrubs were sprayed indoors and transported to 10 sites with known white-tailed deer damage near Ithaca, New York. The shrubs were placed in fields and backyards where deer movement (e.g., tracks in snow) was observed. The researchers checked the shrubs once weekly and photographed damaged yews to measure the amount of deer browsing. They then calculated the surface area of shrubs in each photograph using digital analysis software. To determine significant differences over time, the team applied statistical analysis using analysis of variance models.

Deer repellents that provided the most consistent protection during the study were Big Game Repellent spray, Big Game Repellent mix, Deer-Off, and Deer Stopper II. The performance of other commercial repellents varied considerably among sites, and these products were less reliable. The Japanese pachysandra extracts in experimental repellents CU-A and CU-B were not effective. “By the eighth week of the experiment, all repellents exhibited an average of at least a 30% reduction in surface area, an amount of shrub loss that would not be acceptable to most homeowners. None of the commercial deer repellents tested were effective at repelling deer for more than 6 weeks during the winter”, noted the team. Deer avoided repellents containing putrescent egg solids up to 6 weeks, whereas other repellents tested failed after 4 weeks. The scientists concluded that odor compounds found in the putrescent egg solids were likely responsible for reducing deer damage.

Summarizing the results, Curtis and Boulanger cautioned that although the repellents provide a suitable deterrent if reapplied every 4 to 5 weeks, “if more than three applications of a repellent are required each year for reliable plant protection, homeowners or growers should examine the cost-effectiveness of barrier fencing.” They also noted that repellents cannot be applied with freezing temperatures, or if plants are covered by snow or ice, thus limiting potential applications during winter months in the northern United States and Canada.

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The complete study and abstract are available on the ASHS HortTechnology electronic journal web site:

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Original Article:

Relative Effectiveness of Repellents for Preventing Deer Damage to Japanese Yews
Paul D. Curtis and Jason R. Boulanger
HortTechnology 20:730–734. [Abstract][Full Text][PDF]

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