Based on research conducted since 2014, we have developed a disease favorable day threshold for predicting when a fungicide application in soybean will be economical. The favorable day threshold is based on daily average temperature and hours of high relative humidity, and these parameters are being monitored from weather stations located at Virginia Tech Agricultural Research and Extension Centers (AREC) throughout the state. We have determined that weather conditions approximately three weeks prior to the beginning pod (R3) stage of the soybean crop are the most critical for determining if disease will impact yield and if a foliar fungicide application will be economical. Fungicide recommendations for different locations throughout Virginia can be downloaded below. To use the advisory, follow these steps:
1) Identify the weather station (AREC) closest to your field. A map of the AREC locations can be found here.
2) Download the PDF for your location below.
3) Under the “date” column, find the date that corresponds to approximately when your soybean crop has reached or will reach the R3 (beginning pod) stage).
4) In the row that corresponds to your R3 date, determine if disease risk is low, moderate, or high based on the favorable day threshold.
5) The last column indicates if a spray is recommended based on your R3 date.
Keep in mind that other risk factors also contribute to disease severity and yield loss to fungal diseases. High risk fields include those where susceptible soybean varieties are planted, there is a recent history of soybean foliar diseases, and/or rotations out of soybean are short or soybean is planted continuously over several years. If based on the soybean fungicide advisory or other factors you decide to apply a fungicide, applications are generally the most effective when applied between R3 and R4 stages (no later than R5). The most recent Soybean Fungicide Efficacy Table can be downloaded below.
If you have any questions, feel free to contact Dr. Hillary Mehl (email@example.com).