Comparing the efficacy of delivery systems and active ingredients of deer repellents

Abstract

Deer (Odocoileus spp.) occur across the United States and provide many desirable recreational and aesthetic opportunities. Unfortunately, deer foraging, particularly where population densities are high, can negatively impact agricultural resources or damage ornamental plants . Repellents are often regarded as a desirable approach to limit deer browsing. Although many products are marketed for use as repellents, the efficacy of these products in actually reducing deer browsing is varied. This paper reviews the results from efficacy tests we have conducted at the NWRC Olympia Field Station over the past several years as well as repellent work conducted by others. General efficacies of delivery systems and active ingredients incorporated in a variety of products are compared. Generally, products which have repeatedly demonstrated good efficacy in our trials are those products that produce sulfurous odors . These products have significantly reduced deer browsing for 8 to 12 weeks.

Deer Responses to Repellent Stimuli

“…In laboratory studies, lithium chloride often is used as the toxin to condition aversions (Riley and Tuck 1985). In formulated repellents, thiram (tetramethylthiuram disulfide) is a fungicide used to condition aversions (Nolte and Wagner 2000). Among other symptoms, chronic thiram exposure produces anemia and nausea (Maita et al 1991).…”

“…In practice, repellents employing only bitter compounds are typically ineffective as deer repellents (Nolte and Wagner 2000) and there is some question about the reliability of bitter taste per se as a warning of toxicity (Glendinning 1994;Nolte et al 1994b). Blood and egg are examples of ingredients that yield effective herbivore repellency when applied to plants without causing pain or malaise (Nolte and Wagner 2000). In recent years, hydrolyzed casein (HC) has been added to the list of stimuli that produce long-lived avoidance (Kimball and Nolte 2006).…”

“…However, repellents that rely on neophobia alone (there are no additional negative consequences associated with them) are subject to habituation and will not be avoided for extended periods (Nolte 1999). Visual and vapor repellents often rely on neophobia.…”

“…Chemical repellents also are frequently employed to deter browsing of trees and shrubs by deer in managed systems (Nolte and Wagner 2000). Herbivore repellents are thought to promote avoidance behavior by several different mechanisms or modes of action.…”

“…The consequence of peripheral (oral/nasal/ocular) contact with these repellents is pain. Among mammals, capsaicin is a well-known trigeminal irritant (Nolte and Wagner 2000). Another consequence of ingesting certain repellents is malaise.…”