To be effective, repellents must be applied prior to anticipated periods of deer browsing. Contact repellents are placed directly on the plant and discourage feeding by producing an unpleasant taste. Area repellents are placed in the vicinity of the vegetation and repel deer by an unpleasant odor. Repellents provide cost-effective protection when used in small areas, such as gardens, residential ornamentals, or small orchards. Larger applications for commercial operations have proven too costly, with irregular effectiveness.
Repellents provide effective deer control when they are regularly applied to vegetation.
However, rainfall removes repellents from the vegetation, requiring periodic applications. Changing repellents every few years on each site has been demonstrated to improve repellent effectiveness. The potency of repellents may vary from year to year, and from neighborhood to neighborhood. When deer numbers approach biological carrying capacity, repellents may be totally ineffective. Fences create a barrier between deer and the protected vegetation.