If you have fields where the hybrids aren't as resistant to foliar diseases as you like, then you may want to consider a fungicide application. But be wary of the reproductive phase in corn, as timing the application is essential to get the desired results and avoid injury to developing corn ears.
Bryan Overstreet is an Indiana Certified Crop Advisor and Purdue University Extension ag educator in Jasper County. He is prepared to advise farmers who ask for guidance on if they should spray a fungicide, and if so, when it should be done.
"Most fungicide applications should be made between tassel and brown silk stage," he says. "I would first scout the field to see if it is really needed.
"You need to answer some questions before deciding to spray a fungicide. First, is there disease present on the ear leaf or one or more of the three leaves below it? Second, is it a susceptible hybrid to the disease that has appeared on your crop? Let's assume that in this case it is. Third, was the previous crop in the field corn?"
Knowing if the previous crop was corn can give you a handle on what to expect. Several of the foliar diseases overwinter in corn residue. If the field was in corn the year before there is likely more inoculum present to continue the infestation, assuming weather conditions remain favorable.
"I would also ask some more questions," he says. "Was reduced tillage used? Are current or future expected weather conditions going to be favorable for the disease?
"If all five of these questions are answered yes, you need to spray. If you only answered part of them yes, check again in a week to see fi the treatment is needed," he advises.
Ask your Extension educator about how you can get a copy of Fungicides for Field Crops, which contains lots of good information for decision-making.