UNIVERSITY PARK, Pa. — Many soybean farmers use seeds treated with fungicides to ward off disease, but the profits from these increased yields might not offset the cost of the treatment in most cases, according to a study published in Scientific Reports by researchers at Penn State.
The researchers analyzed how seed treatments affect yield and profitability in soybean farms in the Midwest and found that yield gains were modest and often did not offset the added cost of the treatment. Additionally, financial benefit was likely only when seed treatment costs were low and soybean prices were high.
Paul Esker, professor of epidemiology and of field crop pathology in the College of Agricultural Sciences and lead author on the study, said the findings suggest that growers may want to carefully evaluate the use of fungicide seed treatments on their farms.
"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," said Esker, who is also affiliated with the Plant Institute in the Huck Institutes of the Life Sciences. "Growers may want to use treated seeds only in specific, high-risk situations or after verifying a positive return-on-investment."
The use of fungicide-treated seeds has risen sharply in the last few decades, the researchers said. While about 8% of soybean seeds were treated with fungicide in 1996, that figure rose to 60% to 75% by 2015.
Despite their popularity, Esker said their use may not result in higher profits for farmers. Additionally, he noted, unnecessary use of fungicides could result in potentially harmful effects on beneficial microbes in the seeds and soil.
"Adoption of seed treatments has continued to increase in U.S. soybean production systems, but uncertainty remains about whether their use is necessary," Esker said. "Furthermore, given the parallel questions about the use of seed-treatment insecticides, we recognized that addressing them could go a long way toward helping farmers make better soybean management decisions."
For the study, the researchers analyzed data from both randomized controlled trials and large-scale, on-farm observational studies previously conducted by other teams.
Data from RCTs was limited to studies in the U.S. Midwest that included crop data from both treated seeds and untreated control seeds. Observational data included self-reported information from growers across three growing seasons from 2014 to 2016 and 10 Midwest states.
"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," Esker said.
Analysis of data from randomized controlled trials found an average yield increase of 22.2 kilograms per hectare (kg/ha) — or about 19.81 pounds per acre — that could be attributed to fungicide seed treatments. Analysis of observational data found a similarly small average yield gain of approximately 36 kg/ha, or about or about 32.12 lbs/acre.
Additional simulations showed that these gains in crop yields often didn't offset the costs of seed treatment.
"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 said. "They also will help us collaborate with farmers to determine under what conditions a fungicide seed treatment may be beneficial."
The findings also raise concerns, the researchers said, about the widespread use of fungicide seed treatments on the microbiomes of seeds and their surrounding soil. Seeds and soils have unique compositions of microbes that benefit germination and seedling development, which could be disrupted by unnecessary fungicide use.
"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 said.
In the future, the researchers said the development of tools to assess specific fields' pathogen risk may be a more sustainable and economical approach than the current widespread use of preventative fungicides.
Denis A. Shah, Kansas State University; Spyridon Mourtzinis, Tatiane Severo Silva and Shawn P. Conley, University of Wisconsin-Madison; and Patricio Grassini, University of Nebraska-Lincoln, also co-authored the study.
The U.S. Department of Agriculture National Institute of Food and Agriculture, Wisconsin Soybean Marketing Board, North Central Soybean Research Program, and the United Soybean Board helped support this research.
