Eyespot and Gray Leaf Spot Occurring in Corn

July 15, 2009
ICM News

By Alison Robertson, Department of Plant Pathology

Corn across the state is beginning to tassel and many of you, like me, have been out in fields scouting for foliar diseases of corn. 


The disease of this year, thus far, seems to be eyespot, particularly in central and northern Iowa.  Eyespot loves wet and cool weather so it is probably not surprising that the disease is especially prevalent this year. If such weather continues, we can expect the disease to spread.  

Eyespot tends to be more severe in corn following corn fields, especially if residue is present on the surface. Older corn leaves appear to be more susceptible to infection. The disease usually starts on the lower leaves of the plant and moves up the plant; however, random lesions may also occur in the upper leaves. Hybrids do vary in their susceptibility to the disease.

Initial symptoms are small (one-sixteenth inch in diameter), water-soaked, circular lesions. The lesions enlarge to about one-eighth inch in diameter, and develop a light tan center, dark brown margin and yellow "halo" (photo below). If you hold the leaf up to the light, the halo becomes more apparent, and the center of the spot looks translucent.  Time from infection to symptom development is about 9-10 days.

Early and severe eyespot can result in yield loss on susceptible hybrids.  Furthermore, increased stalk rot severity is associated with severe eyespot disease. 

Gray leaf spot

Gray leaf spot (GLS) is starting to show up on the lower leaves of susceptible hybrids across the state. Tamra Jackson, Extension Plant Pathologist at University of Nebraska — Lincoln, reported GLS is highly prevalent at this time in Nebraska, occurring slightly earlier than normal in that state, and the severity is increasing.  Here in Iowa, the disease is perhaps a little ahead of schedule.  We usually see a few lesions of the GLS on the lower leaves of the plant around mid to late July.  GLS infections in June and early July were associated with the epidemics of GLS in Iowa in the mid 1990s.

GLS disease development is favored by is very warm, humid weather ("Iowa State Fair" weather), and the disease is usually more severe when the previous crop was corn and residue is present on the surface. Like eyespot, GLS usually starts on the lower leaves of the plants and progresses up the plant. 

Lesions of GLS are rectangular in shape (photo below) since the veins of the leaf stop the lesions expanding sideways.  The lesions may develop up to 4 inches in length.  Lesions are initially tan to brown but become silvery-gray when they produce spores. Time from infection to symptom development is about 14-21 days, depending on weather conditions and hybrid susceptibility.

GLS can result in considerable yield loss particularly when the disease spreads to leaves above the ear soon after tasseling. High GLS severity may also increase the risk of stalk rot.

Common rust can also be found in Iowa corn fields this year but at extremely low incidence. Common rust does not survive the winter in Iowa and spores blow into the state from the south each year. This time last year, common rust could be easily found in every corn field. 


The cornerstone of eyespot and GLS management is resistance. Rotation can also reduce risk of disease. Fungicides are also effective at reducing disease and protecting yield.

To determine if a fungicide application is necessary, the following factors should be considered:

• disease pressure in the field

• hybrid susceptibility

• predicted weather conditions during grain fill

• price of corn and cost of fungicide plus application

• previous crop

• field history of disease


Small, circular lesions of eyespot.  Note the yellow halo, dark brown ring and light tan center.



gray leaf spot

Characteristic rectangular gray leaf spot lesions.

Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be reached at (515) 294-6708 or by email at alisonr@iastate.edu.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 15, 2009. The information contained within may not be the most current and accurate depending on when it is accessed.


Alison Robertson Professor of Plant Pathology and Microbiology

Dr. Alison Robertson is a professor of plant pathology and microbiology. She provides extension education on the diagnosis and management of corn and soybean diseases. Her research interests include Pythium seedling disease of corn and soybean and Goss's wilt. Dr. Robertson received her bach...