Below is a link to an excellent article on Northern Corn Leaf Blight. This disease, along with Gray Leaf Spot, is a disease of concern in Iowa. It has been a resurging disease in recent years, and is a disease to keep an eye out for. I am not aware of issues in our northern area corn, but it could appear. The pictures in the article are excellent, and the reference to the table listing fungicides with efficacy rankings is worth looking at and printing off for reference.