There are many different kinds of leaf diseases in corn, including gray leaf spot, Stewart's bacterial disease and common corn rust. You can tell if your corn plants have leaf disease by looking at the bottom row of leaves. If you find brown or dead spots on the leaves, that is a definite indication of leaf disease. There is no cure for leaf disease, but it probably won't cause you much problem because it usually appears after the plant is pollinated and the ear of corn is growing. If you find leaf diseases early in your corn growing, there could be a problem with your soil or the seeds you purchased.
Seed rot is a disease of the corn plant that occurs at the very beginning of the growth of a new corn plant. A seed or a seedling is susceptible to seed rot. One of the sure signs of this corn plant disease is a failure of your corn seeds to sprout. The cause of this might be fungus or bacteria in the soil. If there is a lot of rain after you plant, without proper sun and warmth, the seeds can rot and not sprout due to bacteria growing in the overly moist soil. If the problem is the weather, simply till the soil again and replant in dryer and sunnier weather. If it is a fungus problem, you might need to have your soil tested and then add a fungus treatment.
Corn smut is an issue especially in Midwestern states where storms, wind and hail can remove immature tassels from the ears of the corn. You can find corn smut on plants that you think are growing fairly well. You can identify corn smut by galls or boils growing on or near the ears of the corn; the galls are covered by a whitish membrane. Small galls usually will not wipe out your entire crop of corn, depending on the type of corn you have and the amount of corn you grow.