Evaluation of Two Mammal Repellents Applied to Browse Species in the Black Hills

Abstract

Two mammal repellents, ZAC (zinc dimethyldithiocarbamate cyclohexylamine complex) and TMTD (tetramethylthiuram disulfide) were applied to selected browse species in the Black Hills of South Dakota. Protection was tested by measuring current annual twigs removed during the period of winter use by white-tailed deer (Odocoileus virginianus) and mule deer (0. hemionus). The repellents effectively protected chokecherry (Prunus virginiana), American plum (Prunus americana), aspen (Populus tremuloides), and caragana (Caragana arborescens) from deer browsing. Use by deer on untreated native chokecherry plants varied from 21.8 to 43.9 percent, with a mean of 28.9 percent; use of TMTD-treated plants varied from 2.1 to 17.4 with a mean of 6.8 percent, and use of ZAC-treated plants varied from 0.3 to 1.8 with a mean use of 0.7 percent. Both repellents protected aspen shoots almost as effectively as caging. ZAC was also applied to caragana and plum nursery transplants, and significantly prevented browsing by deer. Mammal repellents provide an alternative to expensive and laborious fencing and caging of experimental plants and plots, and also may be useful in browse revegetation projects. Revegetation of game ranges in the Black Hills of South Dakota frequently has been restricted because newly established plants were consumed before they were large enough to withstand browsing. Large herds of white-tailed deer and smaller herds of mule deer have damaged the browse resource in large portions of winter range areas in the central and northern Black Hills (Berner 1955, Bever 1959). Expensive deer-proof fencing often has been the only way to insure protection for small-scale experimental plantings. Large-scale pilot plantings have not been protected, owing to the great expense. The purposes of this study were (1) to determine if mammal repellents developed for the protection of conifer plantations and commercial orchards also could effectively protect native and planted browse sp cies, and (2) to compare the effectiveness of two commercially available repellent formulations under Black Hills condi-