Research Highlights

Determining Economic Thresholds for Deer Damage

By Laura Temple

Deer like to eat soybeans. In areas with high deer population densities, they can decimate fields. A variety of management strategies have proven to protect yield, but how much can farmers afford to invest in managing deer pressure?

“I have been studying deer pressure in cash crops for years, and I realized that no economic threshold information exists to help farmers determine when it pays to prevent deer damage,” says Cory Heaton, state extension wildlife specialist for Clemson University. “I am working to develop thresholds for deer pressure similar to those provided for other pests.”

The South Carolina Soybean Board is funding Heaton’s efforts to develop economic deer thresholds for soybeans. To define these thresholds, his in-field research seeks to show soybean deer damage as a function of local deer population. He is also working to establish thresholds for other crops, including cotton and peanuts. 

In the process of conducting this research, he has uncovered surprising dichotomies that add to the complexity of managing this wildlife–human conflict.

Data Discrepancies

A crucial step in developing pest thresholds is determining pest population density. Heaton’s team established survey routes about 5 to 8 miles long in agricultural regions of rural South Carolina. Survey teams followed these routes at night to count deer and used the average of three nights of counting to estimate density.

“We learned that deer density in these areas is significantly higher than expected,” he says. “On average, the deer density on the survey routes was 2.5 times higher than the reported county density.”

He notes that in 2022, South Carolina reported the lowest statewide deer population in 40 years. However, local populations in rural areas ranged from 100 deer per square mile to more than 200 deer per square mile. 

To monitor crop damage from deer, his team placed cages in fields along the survey route to protect the crop from deer damage. Throughout the growing season, they compared crop growth and ground coverage in the cages to plots the same size 120 feet from the cages.

“We put cages both at field edges, where high damage is expected, and further into the fields,” Heaton explains. “We realized deer feeding throughout the fields is more uniform than expected.”

From these comparisons, he made initial estimates of the economic impact of deer damage on yields in South Carolina. 

“For example, in 2022, South Carolina farmers lost a rough average of 13 to 14 bushels per acre, or $175 per acre, to deer damage on the 405,000 acres of soybeans planted,” he reports. “In other crops, deer cost 366 pounds of cotton lint and 753 pounds of peanuts per acre.”

These numbers exceed existing data about crop loss to deer. Heaton says most economic information about the cost of deer damage is based on estimates from surveys of farmers, rather than field data. He believes farmers and other forms of gathering this information underestimate the true cost of deer feeding.

Heaton plans to continue gathering data for multiple years to increase confidence in the numbers before recommending thresholds. Like with other pests, those thresholds will account for crop growth stage and other factors. He is on track to develop thresholds that will inform farmers how much they can spend to control deer and maintain profitability. Then farmers can optimize the return on their investments in proven strategies like fencing, repellants and population management that help protect their soybeans and other crops.

Perspectives to Ponder

Heaton seeks to offer solutions to conflicts between humans and wildlife that help everyone involved. However, much like the data differences his research uncovered, finding solutions for deer damage of crops is complex.

For example, deer pressure creates additional challenges for soybean farmers. Heavily grazed soybeans take longer to reach canopy — or may not grow large enough to create a canopy at all. This increases weed pressure. Heaton notes that farmers can struggle to stay ahead of weeds in these fields. He has even talked with farmers who have been put out of business due to deer pressure. 

South Carolina has the longest deer season in the country, running from August 15 to January 1. But state data shows that South Carolina hunters average just one deer per season. Heaton has heard from hunters that deer have been difficult to find or that bait doesn’t consistently attract them. That reinforces the state’s reports that the current overall deer population is low.

He also hears from groups that prioritize protecting deer.

“I want to see wildlife flourish,” he says. “But we need to figure out how to account for local population densities as we tackle this challenge.”

On his own small acreage, Heaton is trying to foster an environment that hosts quail and wild turkeys. He struggles to establish cover and feed for the birds because of deer damage.

“High deer densities, like those found in some agricultural areas of rural South Carolina, negatively impact plant and wildlife diversity,” he adds. “Overpopulation also hurts the deer, increasing food competition and vulnerability to disease. That can become a human health issue.”  

Heaton makes the data from his work available publicly so it can be used to find solutions. He wants farmers to be able to continue farming, hunters to be able to continue hunting, and wildlife to thrive. His hope is that his data can contribute toward those goals. 

He also will share his threshold establishment protocol with researchers in other states. That will help establish local economic thresholds for deer damage in other areas with heavy pressure, much like states do for insect and other pest pressure. 

Additional Resources

• Jeffy Westbury on Deer Pressure in South Carolina – YouTube video
• John Long on Deer Pressure in South Carolina – Vimeo video
• Cory Heaton research video – Facebook

Published: Oct 16, 2023