Applying Fungicide Without Pressure Could Create Resistance – Iowa Soybean Association

Ankeny, Iowa: The Iowa Soybean Association has cautioned farmers that applying fungicides without clear disease pressure could accelerate resistance in soybean pathogens, potentially reducing the long-term effectiveness of these crop protection tools.

According to recent research and extension insights, fungicides deliver the greatest benefit when used in response to an identified disease threat rather than as a routine or preventive measure. Experts warn that indiscriminate or poorly timed applications expose pathogens to repeated chemical action, allowing them to adapt and develop resistance over time.

Scientists have already documented resistance in key soybean diseases. For instance, strains of the pathogen causing frogeye leaf spot have developed resistance to commonly used strobilurin fungicides across multiple U.S. states. This trend highlights the growing risk of overreliance on chemical control without proper disease monitoring.

The association emphasizes the importance of data-driven decision-making. New forecasting tools are being developed to help farmers assess disease risk based on weather conditions and pathogen presence. These tools aim to guide growers on when fungicide application is economically and agronomically justified.

Economic considerations also play a role. Studies indicate that routine fungicide spraying, particularly in low-disease years, may not provide sufficient yield benefits to offset costs, further reinforcing the need for targeted use.

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Agronomists recommend integrating fungicides into a broader pest management strategy, including crop rotation, resistant varieties, and field scouting. By applying fungicides only when necessary, farmers can both protect yields and preserve the effectiveness of these products for future growing seasons.

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