There are several leaf diseases that can infect corn in Kansas in any given year. They can all be controlled with some combination of hybrid selection, tillage management, crop rotation, planting dates, or foliar fungicides.
Soybean planting is around the corner and the best time to protect against seedling diseases is prior to planting! A series of free webinars that will cover soybean seedling diseases and the latest information on fungicide resistance. See this article for more details.