Field Evaluation Of Condensed Quebracho Tannins (CQT) As A White-Tailed Deer Repellent For Soybeans

RALEIGH, NORTH CAROLINA

Ethan L. Marburger, Fisheries, Wildlife, and Conservation Biology Program, Department of Forestry and Environmental Resources, College of Natural Resources, North Carolina State University, Raleigh, NC 27695, USA

Rachel Vann, Department of Crop and Soil Sciences, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC 27695, USA

Guy Collins, Department of Crop and Soil Sciences, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC 27695, USA

James Clothier, Department of Entomology and Plant Pathology, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC 27695, USA            

Christopher S. DePerno, Fisheries, Wildlife, and Conservation Biology Program, Department of Forestry and Environmental Resources, College of Natural Resources, North Carolina State University, Raleigh, NC 27695, USA

Extension Publication Draft

White-tailed deer (Odocoileus virginianus) are responsible for millions of dollars in annual agricultural damages, posing a significant challenge for producers. While chemical and physical deterrents exist, many are ineffective, lack consistent results, and are impractical for large-scale use. Until a practical solution emerges, it is necessary to continually evaluate new options for producers looking to manage the continued depredation and financial losses caused by white-tailed deer. 

Condensed quebracho tannins (CQT) are a naturally occurring secondary metabolite used by plants as a defense mechanism against foraging. Previous research has determined that CQT has the potential to negatively influence the intake rate and probability of consumption in captive white-tailed deer. Given these results, we sought to investigate the efficacy of CQT in a natural field setting as an alternative method to reduce white-tailed deer depredation. 

Our objective was to evaluate the efficacy of CQT sprayed on soybeans as a white-tailed deer repellent to deter browsing on privately owned agricultural land near Black Creek, North Carolina, USA. We selected this site because it allowed us to test our experimental repellent in a real-world agriculture setting with an extensive history of deer depredation. 

Our experimental design consisted of twenty 0.2-hectare plots were randomly assigned to treatment (n = 10) or control (n = 10) (Figure 1). When planted soybeans reached the second vegetative growth stage, treated fields received a single application of our solution consisting of a 10% concentration of CQT and water at a carrier volume of 93.5 liters per hectare. To document white-tailed deer presence and feeding behavior, we placed camera traps in each plot and recorded weekly measurements of soybean height and browsing damage for a period of four weeks after repellent application. 

To fully investigate CQT’s potential as a repellent, we also collected yield data from a particular field on this farm dubbed The Honey Hole. Similar to our other survey methodology (Figure 1), we established 8 alternating 50m x 5m plots, treatment (n = 4) and control (n = 4), with treatment plots receiving a single application of our CQT repellent during the second soybean vegetative growth stage. On October 31, 2024, soybeans from each plot were harvested in 10m strips using a Wintersteiger Quantum Pro Small Plot Combine. The average yield estimates for soybeans harvested in treated plots were 149.76 bushels/hectare, while soybeans in control plots resulted in an average of 152.27 bushels/hectare.

Results indicate that a single application of CQT modestly reduced white-tailed deer browsing on soybeans in an agricultural field setting with moderate to high deer densities (NCWRC 2020) (Figure 2). Compared to control plots, CQT-treated plots experienced statistically significantly less browsing and were 72.9% less likely to be depredated by white-tailed deer, particularly during the second to fourth weeks post-application (Table 1). However, treatment effects diminished over time, and soybean yield estimates were similar between treated and control plots. Additionally, there were no significant differences in the number of deer observed across treatment types. These results suggest that a single application of CQT may not be sufficient to establish lasting avoidance behavior or impact yield under normal field conditions.

While a single application of CQT was able to reduce the likelihood of deer browsing in treatment plots, it may not be sufficient to encounter the majority of individuals in that area. If deer do not rapidly consume CQT-treated plants, negative foraging association and therefore repellent efficiency may diminish as a result of new physical characteristics, such as the emergence of new untreated foliage, which may be selectively browsed by deer over treated foliage, and environmental variables like rainfall. Furthermore, in areas with high deer densities, avoidance of feeding from only a subset of individuals may not be enough to significantly influence yield estimates.

These results suggest that CQT can influence deer behavior in the short term, but sustained reductions in browsing may require repeated applications, higher concentrations, or complementary deterrent and wildlife management strategies. In addition to repeated repellent applications, we recommend that farmers struggling with white-tailed deer depredation employ a combination of methods to alleviate browsing pressure.   ∆