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Student 10-Minute Presentation Competition

Plant-Insect Ecosystems

Student Competition

Student

Grad 10-min Competition: P-IE, Insecticides

Do preventive fungicide and insecticide applications at the R3 growth stage provide a positive return on investment?

Monday, November 10, 2025
8:24 AM - 8:36 AM Pacific
Location: Oregon Convention Center, E147-148, OCC
Oral Presentation Student Competition
Missouri soybean growers commonly apply preventive fungicides and insecticides. Adoption of this practice has increased substantially after soybean rust became a concern in the US in 2004. We evaluated the effect of calendar-based applications of fungicides and insecticides on foliar diseases and insect pests, soybean yield, and return on investment (ROI). Field experiments were conducted at three locations in Missouri during 2024. Fungicides and insecticides were applied either in combination or alone at the R3 soybean growth stage. Weekly insect scouting was conducted from the V4 to R6 growth stages, while foliar disease and defoliation assessments were performed at R5. Additionally, an ROI model was developed to analyze scenarios with and without foliar disease and insect pest outbreaks, including a break-even analysis indicating the scenarios in which the probability of outbreaks would economically justify preventive applications. Low foliar disease incidence was observed across locations, and insect pests did not reach threshold levels. Yield was not significantly increased regardless of the treatment. These preliminary results suggest that, under low incidences of pests and diseases and low probabilities of outbreaks, preventive applications were not cost-effective. Ultimately, we discuss how farmers should consider field scouting, threshold levels, and return on investment as key factors in their decision-making process when deciding whether to apply preventive fungicides and insecticides.