Whereas producers in southern Iowa are looking out for gray leaf spot, those in the northern half of the state should be watching for eyespot development. This disease is caused by the fungus Aureobasidium zeae. 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. Symptoms are small round spots about 1/8 inch in diameter with a brown border and a yellow halo. 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. The best management involves the three standards for corn leaf diseases: resistance, rotation, and tillage. 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. If there is a lot of corn residue left on the surface, it will require more than a year out of corn to significantly reduce the population of the fungus in the field. Tillage can partially control the disease where feasible; this should be considered if hybrid selection and rotation are not feasible or not sufficient.
For more information on eyespot, see ISU Extension publication Pm 963, Eyespot of Corn. You can obtain a copy of this publication from any county extension office or from the ISU Extension Distribution Center by calling 515-294-5247.
This article originally appeared on pages 153-154 of the IC-480(20) -- July 27, 1998 issue.