Comparison of active ingredients and delivery systems in deer repellents

In some situations chemical repellents are a socially appealing nonlethal a lternative to reduce deer (Odocoileus spp.) damage to plants. New products are continually becoming available, but their ability to repel deer is very variable. We tested 20 repellents rep resenting 4 modes of action (fear, p ain, taste, and aversive conditioning) and 2 delivery systems (topical appl ications and area repellents [scent packets]) to evaluate current products and identify trends that could be used to predict efficacy of future produc ts. During fall 1998, Lye placed treated western red cedar (Thuja plicata) seedlings in pastures with black-tailed deer (Odocoileus hemionus) and reco rded number of bites taken from each seedling at weekly intervals for 18 we eks. Four of the 5 most effective repellents used fear as a mode of action. We tested the 5 most effective repellents again in spring 1999 when trees were growing actively and were more palatable to deer. Only Plantskydd (TM) and Deer Away Big Game Repellent (R) powder reduced damage. However, unlik e the winter study, the Deerbuster's (TM) and Bye Deer (R) sachets were hun g on stakes at half the height of the seedlings instead of near the termina l buds. When an additional study was conducted with the sachets mounted nea r the terminal buds so that repellent could drip from bags onto the plants as in the winter study, Deerbuster's sachets and Bye Deer sachets reduced d eer foraging. In general, products using fear as a mode of action were more effective than products using other modes of action and topical repellents were more effective than area repellents.