Soybeans are known to be a preferred food source for white-tailed deer; however, the exact economic impact of deer populations within a given area on the surrounding soybean fields is not known. Just like the number of soybean acreage across South Carolina varies, so does the population densities of deer. The purpose of this project is to affix a predicted dollar value on the amount of soybean damage inflicted by deer feeding as a function of the white-tailed deer population for a given area. Such knowledge will be beneficial for supporting requests on behalf of S.C. growers for addressing the depredation permitting process and for re-assessing season and bag limits. Furthermore, quantification of economic impact as a function of local population will provide a basis for return on investment from damage mitigation; in short, it can assist in development of a guide for break-even costs of deer damage controls.

Results of this proposed study will be disseminated to growers through presentations at grower meetings and field days. Additionally, project results may be included in press releases, social media, blogs, newsletters, scientific publications, fact sheets, and production guides.

Updated April 15, 2021:
During the first quarter of this project study areas were identified and initial deer population surveys were conducted. A total of 4 areas chosen for use in this project. Each area includes multiple agronomic fields, adjacent woodlands, and substantial deer habitat. A spotlight survey route was developed for each study area. Spotlight surveys were conducted 3 times for each route. Surveys were conducted on March 2nd, 4th, and 8th of 2021. Observations for each route were averaged for the 3 nights. Estimated deer densities were as follows: Study Area 1 = 144.0 deer/mi2, Study Area 2 = 144.4 deer/mi2, Study Area 3 = 99.6 deer/mi2, and Study Area 4 = 209.5 deer/mi2. Deer spotlight surveys will be conducted 2 additional times (6 total nights) before the conclusion of the project.

Soybean planting is underway in each study area. Upon germination, deer feeding injury will be surveyed on a regular basis.

Updated July 12, 2021:
Beginning in February, four deer population survey routes were identified in Barnwell County, South Carolina. The spotlight surveys were carried out three times along each route and the average deer population was determined on a square mile basis for each roadway in the routes. Figure 1 shows a portion of the first route with the deer per square mile estimates highlighted in yellow for each roadway along the route. Deer population estimates for each section of roadway surveyed among the routes ranged from 40 deer per square mile to 383 deer per square mile, with an average of 155 deer per square mile. Unfortunately, only one of the four routes surveyed for deer population estimates had soybeans planted along the route. In that particular route five different soybean fields have exclusion cages placed in them for the study. There are total of eleven soybean fields with four different cooperating farmers, and two soybean fields on Clemson’s Edisto Research and Education Center that are enrolled in the project. Each field has four exclusion cages and four plots with out exclusion cages for a total of 104 research plots in the study. Cages were constructed of 48-inch-tall field fence and measure 76 inches by 76 inches since all of the soybeans were planted using a 38-inch row spacing. Weekly aerial pictures are being taken of each plot with a drone to determine canopy closer and deer damage as seen in Figure 2. The weekly images are analyzed using a software program developed at Clemson to count the number of plant pixels and the number of soil pixels in each picture. Before plots are harvested for yield, plant heights and stand counts will be collected. Beginning in a week or so, the second round of deer population estimates will be conducted, excluding the routes that do not contain research plots and adding in the fields that contain research plots.

Figure 1. Displays a portion of the first survey route with deer per square mile estimates for each road highlighted in yellow, along with planting dates and cage assignments for research plots.

Figure 2. Shows an aerial picture taken on July 1st of a caged plot from field 114 that was planted on June 1st.

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Updated October 15, 2021:
“Determining the Economic Impact of Deer Populations on Soybeans in South Carolina”
Since the July update, deer damage assessments have continued via aerial imagery to determine canopy closure as seen in Figure 1. Despite not being able to present this project at a field day this year, there has been much local interest in this research. Cooperating growers and industry stake holders visiting fields in this study have noticed drastic height differences of caged plots and surrounding areas of the field just by visual observations such as those seen in Figure 2. Although no field day was held at the Edisto Research and Education Center this year in Blackville, SC, a write-up of this project was prepared and should be posted to the EREC website in the following weeks. According to the project timeline, everything is right on schedule as damage assessments are being wrapped up and harvest of the plots for yield is about to commence.

Timeline:
? February 2021 – Conduct night time deer surveys
? April 2021 – Construct exclusion cages for research plots
? April – July 2021 – Planting of field trials and initiation of damage assessment
? August 2021 – Conduct the second round of night time deer surveys
July – October 2021 – Conclusion of damage assessments
October – December 2021 – Harvesting of research plots, data entry and analysis
January 2022 – Conclusion of project

A second round of spotlight surveys for deer population estimates in August was postponed to winter because the August timing was thought to not be representative of populations. One survey was conducted at the Edisto REC however, upon conclusion of the survey it was determined that summer-time/growing season surveys would not yield accurate estimates of deer populations. This was discovered after the survey crew observed many deer jumping up from bedding in fields with taller crops, and not being able to accurately count the number of deer in those fields. It was also during this August survey that the crew tested a new computer software designed by Dr. Kirk to aid researchers in accurately recording deer at the location at which they were observed. The software worked very well and will help to ensure repeatability between surveys regardless if the same survey crew is present. This is accomplished by placing a tablet in the cab of a vehicle with a predetermined route loaded into the software program. As the driver navigates the map a GPS receiver is used to determine the vehicles position as the spotlight crew records the deer observed using a manual push button. It is believed that having this software will help researchers to accurately estimate the number of deer on a square mile basis this coming winter when surveys are conducted again.

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Updated December 13, 2021:
Soybean Board December Progress Report for:
“Determining the Economic Impact of Deer Populations on Soybeans in South Carolina”
From the October update until now, the harvest and data collection of all research plots has been completed. A few plots had to be discarded due to damaged cages as seen in Figure 1. It is not exactly clear what damaged the cages but in some cases deer tracks were observed near the mangled cages. Preliminary results of the project were presented at the annual South Carolina Corn and Soybean Growers Meeting held in Santee, SC last week. There was great interest in the project by all attendees at the meeting and audience questions about the project had to be stopped to continue with the rest of the presentations. The timeline for the project is outlined below and is still on schedule as final analysis are being completed in preparation for the final report and the Soybean Board meeting in January.

Timeline:
? February 2021 – Conduct night time deer surveys
? April 2021 – Construct exclusion cages for research plots
? April – July 2021 – Planting of field trials and initiation of damage assessment
? August 2021 – Conduct the second round of night time deer surveys
? July-October 2021 – Conclusion of damage assessments
? October – December 2021 – Harvesting of research plots, data entry and analysis
January 2022 – Conclusion of project

Preliminary analysis of soybean plant heights, and stand counts of caged verses uncaged plots showed a significant difference overall with plant heights, and stand counts being greater in the caged plots. With that said, it was no surprise that the average yield of all caged plots was higher than that of uncaged or check plots (Figure 2). A more detailed analysis will be compiled for the final report in January, along with a proposal for furthering this research in order to obtain more data across the state.

Updated January 17, 2022:

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The main goal for this project was to quantify the amount of soybean damage inflicted by varying deer populations in a given area. To accomplish this, spotlight surveys were conducted to estimate white-tailed deer populations, while exclusion cages were used to determine soybean yield in the absence of deer feeding. Data collection began in February of 2021 with spotlight surveys on the north side of Barnwell County in order to estimate the white-tailed deer populations that were surrounding cooperating farmer’s fields. There were four survey routes that averaged about five miles in length for a total of 20.9 miles. The routes were surveyed three times and the average deer population was determined on a square mile basis for each route. Figure 1 shows a portion of the first route with the deer per square mile estimates highlighted in yellow for each roadway along the route. Unfortunately, only one of the four survey routes had soybeans planted along the route, had this been known earlier in the year routes would have been changed to include more soybean fields. In the route containing soybeans, five different fields were included in the study and had exclusion cages placed in them. There were a total of eleven soybean fields with four different cooperating farmers, and two soybean fields on Clemson’s Edisto Research and Education Center enrolled in the project. Each field had four exclusion cages and four plots without exclusion cages for a total of 104 research plots in the study. Based on consultation with the farmers, half of the caged and check plots were placed in high-pressure areas and half in low-pressure areas. Cages were constructed of 48-inch-tall field fence and measure 76 inches by 76 inches since all of the soybeans were planted using a 38-inch row spacing. Weekly aerial pictures were taken of each plot using a drone to determine canopy closure and possible deer damage. The weekly images were analyzed using a software program developed at Clemson to count the number of plant pixels and the number of soil pixels in each picture. Before plots were harvested for yield, plant heights and stand counts were collected. In the original proposal for the project a second round of spotlight surveys was proposed to be conducted in August; however, after conducting a survey of one route it was determined that summer-time/growing season surveys would not yield accurate estimates of deer populations. During this survey, many deer were jumping up from bedding in fields with taller crops; the survey crew was not able to accurately count the number of deer in those fields. It was also during this August survey that a new computer software application was designed by our Precision Ag group to aid researchers in recording and geo-tagging deer populations. The software will reduce labor requirements to survey and help to ensure repeatability between future surveys. The software operates on a tablet in the cab of the survey vehicle with a predetermined route loaded into the software program. As the driver navigates the map a GPS receiver is used to determine the vehicle’s position as the spotlight crew records the deer observed using a manual push button installed on the spotlights.

The 2021 February average deer population for the routes ranged from 108 to 229 deer per square mile; this is about seven times higher than the most recently published SCDNR estimates for Barnwell County according to a 2013 SCDNR deer density map. Yield data from exclusion cages and control plots suggested that deer were on average responsible for a 14 bu/ac loss as seen in Figure 2. In Figure 3 the yield data is shown by field and excluding the CR field there is a 10.6 bu/ac difference in yield on average. Figure 4 is the same data displayed as a percentage loss per field with an average loss of 18.2% if the CR field is excluded. It should be noted, however, that the CR field was not found to be a statistical outlier.

One goal for this project is that the night surveys coupled with crop damage data could lead to recommendations being made on deer depredation tags issued to farmers for a given field. Typically, there are only ten depredation tags issued for every fifty acers of crop planted, but this is a case by case basis and is determined by DNR. Typically, it is not the larger fields that are hit the hardest by deer feeding but the smaller fields that have a larger edge effect. Having the data to determine the economic impact of deer population on surrounding soybean fields could prove valuable to growers requesting depredation tags. It is suspected that the economic data collected here could also be used to support requests to the state for other measures to reduce deer populations, such as an extended hunting season, increased limits, etc. Determining economic impact as a function of local population will also provide a basis for implementing cost effective deer damage controls. In the absence of such knowledge, it is difficult for a farmer to know the return on investment from control measures.