There has been promotion in the marketplace the value of applying a fungicide early season.  However, research from Universities has shown that the greatest benefit comes from applying a fungicide application at tasseling and on provided that fungicide is needed.
The promotion of early season fungicide applications have been from the fourth leaf collar stage to eight leaf collar stage.  Yes, one can say there is the advantage of throwing this in the tank-mix as one applies a herbicide, but early applications do not provide much value.
Results from across the Corn Belt indicate that an early season application does not provide the value compared to one applied late season.  The best use of fungicides late season is where disease pressure is present and the corn hybrids are susceptible to the target disease.
Hybrids that contain resistance to diseases such as gray leaf spot have little chance of yield response from a fungicide application targeted to that disease.  First step in disease management is the selection of resistant hybrids.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.