Research Highlights

Research Highlights
3D Scouting Tool Improves Accuracy of Soybean Defoliation Estimates

By Laura Temple

Scouting serves as the primary defense farmers have against insects. Entomologists have set a variety of thresholds for different pests to help farmers determine when treatment is needed to protect soybean yield.

In the case of leaf-chewing insects like beetles, caterpillars and grasshoppers, estimating percent leaf defoliation serves as a scouting shortcut. However, the human eye isn’t very good at estimating defoliation levels, according to Kelley Tilmon, professor of entomology at Ohio State University.

“We’ve established defoliation thresholds at various growth stages that trigger when farmers should treat to control insects,” she explains. “For example, during pod development and fill, soybeans can tolerate 10% leaf defoliation. But it is harder to determine what that looks like than it sounds.”

Thanks to soy checkoff support from the North Central Soybean Research Program, or NCSRP, and the Ohio Soybean Council, Tilmon and her team developed a tool to help estimate soybean defoliation levels. A set of 3D-printed soybean leaves visually show 30%, 10% and 15% defoliation, the thresholds at the V1 to R2 growth stages, R3 to R5 and R6 respectively. 

“We developed an exercise using this soybean defoliation leaf guide and tested it in Ohio prior to the 2023 growing season,” Tilmon says. “We found an average of 35% improvement in the accuracy of estimating defoliation with these model leaves, compared to estimates made without any aid.”

She believes farmers tend to overestimate defoliation levels, so using this tool can save time and input costs that might otherwise be spent on unnecessary insecticide applications. It also guards against underestimating defoliation levels, helping protect soybean yields.

Northeast Iowa farmer Suzanne Shirbroun agrees. She serves as president of the NCSRP board, and she has used the tool and shared it with others.

“Most farmers overestimate insect damage – they think it looks worse than it is,” she says. “Personally, I tend to underestimate defoliation. Either way, something about touching and holding examples of 10, 15 and 30% defoliation makes a big difference in understanding what that looks like.”

Shirbroun believes the 3D-printed leaves and the insect identification card distributed with them are practical tools to keep in the glove box of the truck. These tools also reinforce the value and relevance of research funded by the soy checkoff.

“When we have defoliating insects like grasshoppers or caterpillars in our fields, we can better estimate how much damage is being done to determine if treatment is needed or not,” she explains.

To support this effort, the Soybean Research and Information Network, or SRIN, has printed more than 10,000 copies of the guides and shared them with state and regional soybean checkoff organizations for distribution. 

Published: Jun 19, 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.