Insect Management: Refining threshold to protect soybean yield

Insect management is important in soybean production, but it can be hard to know when to treat. Spraying too early or when it isn’t needed adds extra cost, while waiting too long can lead to avoidable yield loss.

Soybean plants have the ability to tolerate certain levels of injury, but this tolerance varies depending on growth stage, type of damage, and environmental conditions. Without accurate thresholds, growers may overestimate the need for treatment.

This project evaluated defoliation and stem-feeding injury to better define economic thresholds under South Carolina growing conditions.

Leaf-punch tool created using a 3-D printer was used to punch holes in leaflets and simulate defoliator injury

As a result of this project, Clemson researchers delivered:

• Field trials simulating defoliation and stem-feeding injury at multiple growth stages

• Quantification of yield response to varying levels of insect damage

• Evaluation of natural insect populations under field conditions

• Data to refine treatment thresholds based on economic impact

• Improved guidance for scouting and decision-making

Simulated defoliation and natural infestations of stem-feeding insects were monitored and evaluated throughout the growing season. Researchers compared treated and untreated plots to determine the impact of insect pressure on plant health and final yield, then applied insecticides at varying thresholds to assess the effectiveness and economic return of different management strategies.

PhD student Adam Whitfield applying insecticide 

Across all trials, one of the most consistent findings was that insect presence alone is not a reliable indicator for treatment. In many cases, insecticide applications did not result in a yield benefit unless pest populations exceeded economic thresholds. This reinforces the importance of using threshold-based approaches rather than preventative applications.

Future work will focus on expanding these trials across additional environments and pest complexes, as well as continuing to refine thresholds under varying production conditions. Additional outreach will also be conducted to improve adoption of these practices among growers.

The key takeaway for growers is that effective insect management depends on accurate scouting and threshold-based decisions. Applying insecticides only when economic thresholds are reached can reduce costs, preserve beneficial insects, and maintain yield potential in South Carolina soybean systems.

This information is from the 2025 research project, Simulating Defoliator Injury Thresholds, Stem-Feeder Injury Thresholds, and Natural Pest Population Thresholds. The lead was University of Clemson researcher Dr. Jeremy Greene. Project sponsored by the South Carolina Soybean Board.