A new Penn State study finds that fungicide-treated soybean seeds produce only small yield gains that usually don’t cover treatment costs. Researchers say farmers may be better off cutting input expenses than banking on chemical seed coatings.
A widespread practice among soybean farmers — coating seeds with fungicides before planting — may be costing more than it earns, according to new research from Penn State published in Scientific Reports. The study found that yield increases attributable to fungicide seed treatments were modest at best, and in most scenarios, those gains failed to justify the added expense.
What the Research Found
Researchers examined how fungicide seed treatments affect both crop yields and farm profitability across the Midwest, drawing on two types of data: randomized controlled trials and large-scale, on-farm observational studies. Randomized trial data pointed to an average yield increase of roughly 22.2 kilograms per hectare — about 19.81 pounds per acre — linked to the treatments. Observational data showed a similarly small average gain of around 36 kilograms per hectare, or about 32.12 pounds per acre.
Simulations built on those numbers consistently showed that such marginal yield bumps were unlikely to cover the cost of the seed treatment under typical conditions. Profitable outcomes appeared only when treatment costs were especially low and soybean market prices were unusually high.
Lead author Paul Esker, a professor of epidemiology and field crop pathology in Penn State’s College of Agricultural Sciences, said the data challenge assumptions that many growers hold about the value of preventive treatments.
“Farmers often talk about putting money in their pockets, and our research suggests that this can occur by reducing input costs rather than by assuming an economic gain from using treated seeds,” Esker, who is also affiliated with the Plant Institute in the Huck Institutes of the Life Sciences, said in a news release.“Growers may want to use treated seeds only in specific, high-risk situations or after verifying a positive return-on-investment.”
A Rapidly Growing Practice Under Scrutiny
The scale of fungicide seed treatment adoption makes these findings particularly significant. While roughly 8% of soybean seeds were treated with fungicide back in 1996, that share had climbed to between 60% and 75% by 2015.
“Adoption of seed treatments has continued to increase in U.S. soybean production systems, but uncertainty remains about whether their use is necessary,” Esker added.
The research team designed its analysis to go beyond simple correlations. By combining controlled experimental data with real-world farm observations, the team aimed to give growers more actionable guidance.
“This approach moves us away from a purely correlative interpretation of the results and aligns more closely with the questions that farmers often ask us,” added Esker.
Environmental Concerns Add to the Case for Caution
Beyond the financial argument, the study raises ecological flags. Seeds and soils host complex communities of microbes that support germination and early plant development. Routine, indiscriminate use of fungicides could disrupt those microbial communities even when no disease threat is present — a cost that doesn’t show up on a farm’s balance sheet but could affect long-term soil health.
Esker said the findings strengthen the case for a more targeted approach.
“Our results add to a growing body of evidence that fungicide seed treatments do not provide consistent, reliable protection against downside yield loss risk,” Esker added. “They also will help us collaborate with farmers to determine under what conditions a fungicide seed treatment may be beneficial.”
Looking ahead, Esker called on policymakers to take note.
“Given the small economic benefits and these known ecological risks, policymakers may want to prioritize support for research and extension programs that help growers identify the specific conditions where seed treatments are likely to be profitable,” Esker added.
Why It Matters
For agriculture students, agribusiness majors and anyone interested in sustainable food systems, this study offers a concrete example of how deeply entrenched farming practices can persist even when the economic and environmental evidence doesn’t fully support them. It also illustrates a broader tension in modern agriculture: the pull toward preventive chemical inputs versus the push for precision, data-driven decision-making.
The researchers suggest that developing field-level tools to assess pathogen risk could offer a more sustainable and cost-effective alternative to blanket preventive treatment — a direction likely to shape the next generation of crop management strategies.
Co-authors included Denis A. Shah of Kansas State University; Spyridon Mourtzinis, Tatiane Severo Silva and Shawn P. Conley of the University of Wisconsin-Madison; and Patricio Grassini of the University of Nebraska-Lincoln.
Source: Pennsylvania State University