Northern Corn Leaf Blight (NCLB) is being found in area corn fields at low levels now. Here is a picture of a couple of leaves brought to me by local crop consultant David Wagner, showing NCLB lesions.
NCLB causes these dark tan, cigar shaped lesions that often begin on the lower leaves of a corn plant. If you find this disease in a corn field, it does not necessarily mean that you need to spray a fungicide.
Below is an excerpt from the 2015 UGA Corn Production Guide that discusses NCLB.
Although fungicides are important tools for the management of northern corn leaf blight, growers should understand that simply finding this disease in small amounts does not necessarily mean a fungicide application is needed. Nearly every field in the state will have some level of northern corn leaf blight; timely fungicide applications are advised in situations where this disease is likely to develop further. Such occurs most often when a susceptible variety is planted and conditions are favorable for disease development (e.g., ample rainfall).
You can find the entire 2015 UGA Corn Production guide at http://www.caes.uga.edu/commodities/fieldcrops/gagrains/documents/2015CornProductionGuide.pdf
Growers should scout their corn fields for NCLB and only consider treating with a fungicide if conditions are favorable for the disease to spread.
If you have any questions about NCLB, contact your local county agent for more information.