In 2007, many acres of corn in Wisconsin were sprayed mid-season with fungicides: strobilurin or a strobilurin/triazole combination (in Iowa and Illinois an estimated 6 million acres of corn were sprayed). Most acres applied had little or no disease at the time of application. Reasons for spraying vary and include the high price of corn, potential to control diseases and a possibility of improved yield from plant health benefits. Until this year, fungicide applications to production cornfields were rarely practiced because they were not profitable. Many of the hybrids grown today have good overall tolerance to foliar diseases.
Results of fungicide trials have been mixed in Wisconsin. In two of 11 trials, a significant yield response occurred that covered the fungicide cost.
Some plant damage has been reported when using fungicide – some of it severe. There is no confirmed correlation between damage and fungicide. There is no real evidence that continuous corn (no- and strip-till), routinely needs fungicide more often, but anthracnose and gray leaf spot inoculant potential is higher. Fungicide damage was related to weather and crop conditions in 2007, but it could happen again, so you may not want to apply pre-tassel.

Continue Reading on the Wisconsin Corn Agronomy Extension site