Fungicide Application to Manage Soybean Foliar Disease in Oklahoma: Is it worth it?

In Oklahoma, although foliar disease development is not favored every year, many soybean growers still apply preventive fungicides with inexpensive active ingredients, such as tebuconazole. However, the economic return on these applications remains uncertain and depends on factors like disease pressure, environmental conditions, fungicide costs, and crop prices. Due to that, data from 25 uniform fungicide trials (UFTs) conducted from 2005 to 2024 at different locations across Oklahoma were compiled to determine the efficacy and profitability of fungicides applied at R3: QoI, DMI, QoI + DMI, and QoI + SDHI. A network meta-analytic model was fitted to defoliation (%) caused by foliar diseases, such as Septoria brown spot and Cercospora leaf blight, and to the non-transformed mean yield for each treatment, including the nontreated. The average yield across UFTs was 2,974.7 kg/ha, ranging from 678.8 to 4,832.4 kg/ha, while average defoliation was 39.51% (range: 1.7–99%). The yield response (kg/ha) relative to the nontreated was 67.5 for QoI + DMI, 81.8 for DMI, 122.6 for QoI, and 272.2 for QoI + SDHI. The probability of breaking even on fungicide and application costs was calculated under different price scenarios. Although fungicide applications increased yield, all probabilities remained below 50%, with the highest for QoI (41%) and the lowest for QoI + SDHI (27%). Results indicate that in Oklahoma, foliar fungicide applications are unlikely to break even and are not an economically viable option for managing soybean foliar diseases.