Research Highlights

Research Highlights
Fitting Forage Soybeans into Deer Management Strategies

Deer feeding in forage soybean trial fields. Photo: Luke Macaulay

By Laura Temple

Protecting soybeans from deer damage can be complex, due to great variation in fields, the environment and even deer behavior, according to Luke Macaulay, Ph.D., wildlife management specialist with the University of Maryland. However, bare spots along timberlines and yield maps provide plenty of evidence that damage from deer can be costly. 

Macaulay shares that according to USDA data, deer damage cost farmers about $10 million in 2012 in Maryland, and many consider that an underestimate. As with any pest, he recommends farmers take an integrated pest management approach to protecting their crops from deer.

“IPM tools for deer management include fencing, repellants, vegetation management and hunting,” he says. “We are currently learning more about how we can use forage soybeans as a vegetative management tool.”

With checkoff funding from the Maryland Soybean Board and the Delaware Soybean Board, Macaulay is leading a study to learn more about how and where forage soybeans have the greatest potential to limit deer feeding on commodity soybeans. Building on previous work, his research combines comparing forage soybean options with observing deer behavior, providing guidelines to optimize the value of this strategy.

Deer Feeding Tendencies

Macaulay explains that deer prefer to feed in spaces close to escape cover that feel safe. This includes edges of fields near tree cover, brush and tall grass. He has observed deer using slight changes in field topography as preferred grazing areas, taking cover behind small raised areas or in small swales where they are less visible from the far side of the field. About 75% of their grazing activity throughout the season happens after sunset. 

“Deer will eat whatever is in locations they like first,” he says. “While the study looked at differences in deer preference between forage soybean varieties, at this time, location seems to outweigh variety preference. We have not yet been able to quantify statistically significant differences in grazing between forage soybeans.”

Farmers choosing to use forage soybeans to limit deer damage should consider planting them along edges of fields with these characteristics, or in places with known deer feeding in the past. 

On average, 75% of deer feeding occurs after sunset, as shown by the timing of photos triggered by deer activity in trial plots. Source: Luke Macaulay

Macaulay reminds farmers that up until World War II, soybeans were raised for livestock forage. Forage soybeans produce more biomass than varieties grown for protein and oil content. When grazed, forage varieties regrow and branch out even more. Forage soybeans can be harvested with commodity soybeans, but that works best when the maturity groups of the varieties align.

“However, farmers should consider factors beyond harvest timing when choosing a forage variety,” he continues. “Our observations show that deer eat leaves before they eat soybean flowers and developing pods, but they still account for their comfort and accessibility.”

He points out that soybeans can recover and even benefit from moderate deer grazing, especially during vegetative growth, because soybean plants compensate with additional growth and branching. His team observed that moderate deer grazing increased biomass of soybean plants. 

However, when deer graze soybean seedlings below their cotyledons, they kill the plants entirely. Thus, protection is crucial at the early seedling stage. Other research has shown that soybean defoliation at the flowering and early seed pod formation stages also impacts yield more than at other vegetative and reproductive stages, Macaulay says. He notes that gestating and lactating deer have higher caloric needs, leading to a sudden increase in grazing in late spring and early summer, which often coincide with soybean planting and early growth.

Macaulay notes that planting later-maturing forage soybean varieties may help reduce grazing on conventional soybeans during their more vulnerable early reproductive stages, since those forage soybeans would be in vegetative growth stages later into the summer. Placing such varieties where deer like to feed can be most effective in minimizing damage to the primary soybean crop. 

If farmers have a sufficiently sized area they want draw deer to, his team has anecdotally observed that deer will focus their grazing in the same area where the first-planted soybeans emerge. Planting forage soybeans a few days before conventional soybeans will attract deer to that area of the field. If that field space is adequate and the crop isn’t completely destroyed, deer seem to stay in that area, alleviating damage elsewhere.

“In a farmer survey, forage soybeans rated an average 7 out of 10 for effectiveness,” Macaulay says. “While they aren’t a silver bullet, forage soybeans can be a useful tool. We will continue this research to gather more data to better understand variations between growing seasons.”

Based on data from this ongoing research, Maryland has developed a cost-share program to help farmers plant forage soybeans.

Synergies with Additional Deer IPM Tools

However, Macaulay cautions farmers that forage soybeans should be just one part of an overall IPM strategy. 

“Forage soybeans essentially provide deer with free food,” he explains. “This can increase the carrying capacity of an area for deer population, so forage soybeans should be coupled with a hunting program to manage deer population density.”

Jim Lewis, University of Maryland extension agent and farmer, is working with Macaulay on this project. He has found that forage soybeans can be integrated with deer population density management. Instead of harvesting forage soybeans, he leaves them on the edge of fields, providing a feeding spot that often draws them out during hunting season, which hunters appreciate.

Deer activity, as determined by photos triggered in trial plots, tends to peak a few days after rainfall, when soybeans are putting on new growth. Source: Luke Macaulay

As the team studied deer behavior and counted deer feedings in various plots, Macaulay uncovered a few unexpected tendencies that can help farmers design a deer management plan that works for their farms.

“Across all our plots, we saw surprising spikes in deer activity a couple days after rainfall,” he reports. “Deer appeared to be more willing to come out in the open to feed when soybeans were in prime condition and putting on fresh new growth, a couple days after a rain. This activity accounted for about 45% of their grazing throughout the season.”

For farmers who also use a repellant program or fencing, they can aim to apply repellant or check fences shortly after a rain. Timing these efforts could better deter deer when they are more likely to enter soybean fields. 

Additional Resources:

Cory Atkins on Wildlife Management – YouTube video

Jeffy Westbury on Deer Pressure in South Carolina – YouTube video

Danielle Bauer on Deer Management in the Mid Atlantic – YouTube video

Published: May 8, 2023

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.