Across North Carolina, soybeans are currently at a range of growth stages, from flowering (R1-R2) to nearing full seed (R5-R6). Often, this is when we begin to see an increase in foliar disease pressure and need to make decisions about if and when to apply a fungicide. However, several factors influence disease risk, including soybean variety, field history, environmental conditions, and planting date. These factors should all be considered when making fungicide application decisions.
In North Carolina, frogeye leaf spot (FLS) (Figure 1) is one of our most yield-limiting foliar soybean diseases, but the impact of this disease can vary from year to year and from location to location across the state. Therefore, it can be challenging to determine what disease risk looks like throughout the season, particularly during critical grain-fill periods.
Recently, the Crop Protection Network (CPN) launched a new resource, Crop Risk Tool, that determines the level of risk for a variety of crops and diseases at specific locations across the United States. This tool is free to use and is designed to help enhance disease management decisions. Figure 2 shows a snapshot of the tool with three locations across North Carolina selected, displaying the increase in FLS risk throughout the 2026 season.
Additionally, the NC State Extension Soybean Pathology program has been evaluating optimal fungicide application timings. Fungicides are recommended to be applied between R1 and R5 and are primarily applied between R1 and R3. However, with the wide range of planting dates and maturity groups in North Carolina, the objective of recent studies was to investigate optimal application timings to protect yield and suppress FLS in soybeans.
In 2024 and 2025, a total of seven field experiments were conducted across three locations in North Carolina. Treatments consisted of three application timings (R1, R3, and R5) and a non-treated control (NTC). Low to moderate disease occurred in 2024 across all field experiments, primarily due to dry weather throughout the season, which delayed the onset of FLS. In 2025, moderate to high levels of disease occurred as environmental conditions were more conducive to disease development.
Across all experiments, fungicide applications at R3 and R5 resulted in statistically (α=0.05) higher yields compared to the R1 application and NTC (Figure 3). With the trend of delayed FLS onset and increased disease pressure occurring at later growth stages, applying a fungicide at the optimal timing can help protect yield during critical grain-fill periods.
As we move through the season, consider using the CPN Crop Risk Tool along with field history, variety, planting date, and current environmental conditions to help make informed fungicide application decisions.
