Fungicides can be an effective tool in fighting against yield losses caused by fungal pathogens. The timing of these applications play a major role on their effectiveness.
Always read and follow label instructions for all pesticide applications.
Corn

Maximize efficiency by understanding differences in hybrid susceptibility, weather, and field history
Mid-vegetative (V5-V8): Mixed data but often considered secondary and less effective versus a VT application. Frequently done in unison with a nutrient foliar application
VT (Tassel and pollination): Highest ROI at or shortly after tassel when majority of diseases start to spread
Safe to apply a fungicide with a non-ionic surfactant when majority of the field is at VT
Mid-vegetative (V5-V8): Mixed data but often considered secondary and less effective versus a VT application. Frequently done in unison with a nutrient foliar application
VT (Tassel and pollination): Highest ROI at or shortly after tassel when majority of diseases start to spread
Safe to apply a fungicide with a non-ionic surfactant when majority of the field is at VT
Soybean

As with corn, knowing susceptible fields and varieties will help maximize fungicide efficiency
R3 (beginning pod): The main window of application for highest ROI is around the R3 growth stage
Insecticides can be tanked mixed with a fungicide application at this time if conditions and pest pressure warrant it
R3 (beginning pod): The main window of application for highest ROI is around the R3 growth stage
Insecticides can be tanked mixed with a fungicide application at this time if conditions and pest pressure warrant it