In the University of Illinois Extension Pest Management and Crop Development Bulletin No. 15 released July 3, 2008, University of Illinois Crop Sciences Professor Carl Bradley discussed "Making Profitable Fungicide Applications in Corn." His article began, "In 2007, a record number of corn acres were sprayed with foliar fungicides in Illinois and other Midwestern states. A similar trend is expected for 2008. But are all these applications necessary? The simple answer is no, because a foliar fungicide application to corn will not always provide a yield (or economic) benefit."

Bradley laid out several risk factors that increase the chance of a corn field developing a severe foliar disease problem:

• Previous crop and tillage practice. When corn was the previous crop and a substantial amount of residue is left on the soil surface, the risk of foliar disease increases. Many of the fungal pathogens that cause foliar diseases on corn survive in corn debris.
• Planting date. Research conducted by Dr. Gary Munkvold at Iowa State and Ron Hines at the University of Illinois Dixon Springs Center indicated that late-planted corn is more at risk to gray leaf spot that early-planted corn.
• Hybrid susceptibility. Most hybrids are rated for their susceptibility to diseases like gray leaf spot and northern corn leaf blight.
• Weather and environment. High relative humidity and moisture are important for the development of foliar diseases on corn.
• Disease observations. Scouting fields prior to tassel emergence may give an indication of potential disease pressure. The earlier that some diseases are apparent, the greater the risk of losing yield. This is especially true for rust. No hard and fast economic thresholds are available for foliar corn diseases, but scouting can give an indication of how quickly diseases are building on the lower leaves.
• What about hail-damaged corn? The fungi that cause foliar diseases of corn do not need wounds to cause infection on the leaves, nor is there any evidence that wounds even favor infection by these pathogens.
• What about yield increases despite lack of disease pressure? As a plant pathologist, this is a question that I hate to tackle, because it is actually an issue of plant physiology that has nothing to do with plant pathology. That being said, it is true that some fungicide classes can have other impacts on plants besides disease control.

Professor Bradley concluded his article, "Overall, foliar fungicides are a great disease management tool to have available for corn production. With escalating commodity prices and the demand for greater yields, we are all looking for ways to bump corn yields: however, there are no silver bullets. Foliar fungicides can help increase production and profits, if they are used appropriately."