The NC State Soybean Extension and Pathology programs conducted foliar fungicide trials across North Carolina in 2023. Field trials were located in Sampson, Union, and Yadkin counties (Figure 1) and the trials included seven different fungicide products applied at R3 with various fungicide products plus a nontreated control as a check (Table 1). A soybean variety that was moderately susceptible to frogeye leaf spot was used across locations.

Table 1. Fungicide Products, Active Ingredients, and Fungicide Resistance Action Committee (FRAC) Code.

Weather conditions and disease pressure varied across the locations. Generally, for infection and reproduction most pathogens favor a high relative humidity (>80%), warm temperatures (75-85 F), and are dispersed within and across fields from wind and rain splash.

These weather conditions were collected for each location from July 1, 2023 to August 30, 2023 to capture environments that may be favorable for diseases before and after fungicide applications occurred. Sampson and Yadkin both had a higher and more consistent relative humidity compared to Union (Figure 2). Though Sampson and Union experienced higher temperatures than Yadkin (Figure 3). Sampson also had the highest amount of rainfall compared to the other two locations (Figures 4 and 5). A disease can only occur if it has the three components; a susceptible host, a conducive environment, and the fungal organism causing the disease must be present. Without these three points, disease will not be observed, however the factors within each of these components can influence the risk and pressure of disease that we may see. For example, if a resistant variety has been planted, we may still see disease as the host may not be completely resistant. The same is true for the environmental components influencing disease pressure and this was observed based on the weather data collected. Sampson county was the only location with all three factors favorable for disease development.

Below are the yield results for how the various fungicide products performed across and within the locations with varying environmental. There were no statistical differences between the fungicide application (combined across products) and the nontreated control across all locations (Figure 7). Though, within each environment Sampson did show that fungicide protected yield significantly compared to the nontreated check (Figure 8). There were no differences observed in Yadkin or Union (Figure 9 and10).