Farmers are frustrated by deer feeding on soybeans, but spraying repellents to deter browsing simply doesn’t work.

Deer pose a significant threat to soybean yields across many regions, with their browsing habits leading to considerable crop damage. To combat this, various deer repellent products are available, each claiming to effectively deter these unwanted grazers.

Over the past two years, Grady Rogers, a University of Missouri graduate student in plant science, tackled the topic and company statements to assess if the products deliver on their promises.

Despite the high expectations set by the manufacturers of these repellents, Rogers' research indicates that their effectiveness in soybean fields is limited. The lack of significant improvement in browsing deterrence suggests that these products are not a viable long-term solution for mitigating deer damage in soybeans.

MU Extension weed scientist Kevin Bradley emphasizes that the practicality and economic feasibility of the repellent products also remain questionable.

“In this research, we sprayed these products in probably an unrealistic manner, every three weeks or so,” he says. “I don't know how somebody can afford to do that in soybean setting. And then keep in mind that we didn’t see any differences between these products.”

Project at a glance

Rogers structured the research around two main objectives. The first was to evaluate if mixing deer repellents with herbicides affects weed control and crop injury. The second was to determine if these combinations reduce deer browsing.

The study encompassed three fields: two focused on browsing and one on weed control. Rogers evaluated four different repellent products, including Liquid Fence, Bobbex, Hinder and PlantSkydd, each made from various aromatic compounds such as egg solids, garlic oil and bovine blood.

CAGE MATCH: After a two-year study at the University of Missouri, the only way to protect soybeans from deer browsing is a wire cage. There is a stark plant height difference from those inside and outside of the structure, but fencing farm fields is cost-prohibitive. (Photo by Mindy Ward)

The repellents were tested in different application frequencies (preplant, V3-V4 and R1-R2 stages) to assess their effectiveness.

For browsing evaluation, Rogers used exclusion cages to create a control with zero browsing. The remaining plots were treated with repellents and compared to herbicide-only treatments. In the weed control field, he tested whether combining herbicides with repellents affected the efficacy of weed management.

Results and insights

Analysis of browsing data revealed that none of the repellent products demonstrated a statistically significant advantage over the herbicide-only treatments.

The data from both the West and East Rangeline Drive test fields showed that the repellents did not significantly reduce deer feeding compared to the controls. The only true deterrent was inside exclusion cages. Still, deer browsed up to and around it. Yields from plots treated with repellents were comparable to those with herbicide alone.

HOOF PROOF: The deer population around MU’s Bradford Research Farm continues to grow and create problems for researchers. (Photo by Mindy Ward)

Applying these products every three weeks, as recommended, was not only impractical but also not cost-effective for many growers. The cost of some repellent products can be as high as $40 per acre.

Despite dire efforts to control deer in soybean fields, Bradley says repellents do not seem to be the answer.