In the United States, white-tailed deer (Odocoileus virginianus) and other ungulates cause millions of dollars in annual crop losses, posing a substantial challenge for producers. Although chemical and physical deterrents exist, many are ineffective, lack empirical evidence, or are impractical for large-scale use. Condensed quebracho tannins (CQT), a naturally occurring secondary plant metabolite, are used in ruminant feeding trials and may deter foraging. Prior research has shown that CQT reduced intake rate and consumption probability in captive white-tailed deer. Our objective was to evaluate the efficacy of CQT sprayed on soybeans as a white-tailed deer repellent in a natural field setting near Black Creek, North Carolina, USA. Twenty 0.2-hectare plots were randomly assigned to treatment (n = 10) or control (n = 10). Treated plots received one application of a 10% CQT solution at 93.5 liters per hectare. Camera traps recorded deer presence and foraging, and weekly measurements tracked soybean height and browsing damage. Results showed a single CQT application reduced deer browsing, particularly during weeks 2 to 4 post-treatment. Compared to control plots, CQT-treated plots saw a significant 72.9% reduction in browsing. Soybean height in CQT-treated plots was similar to plants protected in fenced enclosures during the first 2 weeks, indicating suppression of browsing pressure. However, repellency effects declined over time, and final yield (bushels/hectare) estimates did not differ between treatments. No significant differences in observed deer behavior were detected, suggesting that one application may not produce lasting avoidance or improve yield. Repellent effectiveness appeared to diminish along with visual evidence of tannin residue on soybeans after two weeks post application. Future research should explore more frequent applications, alternative delivery systems to maximize contact with treated plants, and integration with broader management strategies.
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