Conditions were good for eyespot in June, and it became prevalent in central Iowa. Recent hot weather is probably slowing this disease down considerably, and it is not severe yet in most fields. Still, it had an early start and is capable of causing significant yield losses. Eyespot can be confused with another disease, Holcus spot, but Holcus spots are all different sizes, very pale, and may or may not a have a brown border. See the June 29 ICM newsletter article, Corn leaf diseases appearing , page 124, for more information on Holcus spot.
Eyespot causes small, round spots with a brown border surrounded by a a yellow halo.
At this point there is little that can be done about eyespot. It is too late to apply Tilt in most fields, and we have very little data on the profitability of using Tilt for eyespot in hybrid corn. There are no hybrids that are highly resistant, but there are some that are partially resistant. Check seed company ratings for this information. Rotation with any crop other than corn will reduce the risk of disease.