Gray Leaf Spot (GLS) is a fungal disease that can cause significant yield loss in corn when conditions are right. 

This disease develops rapidly under warm and humid conditions.  GLS is more prevalent in the Midwest and the Eastern portions of the U.S., but it has established itself in the drier High Plains where, under irrigated conditions, the microclimate in these irrigated fields is warm and humid. 

The fungus overwinters on crop residue, so with more and more no-till or minimum-till farming practices, there can be ample inoculum to infest a corn crop. 

GLS lesions typically show up on the lower leaves first, as spores spread from the crop residue onto the plant.  These lesions are distinct elongated tan to gray, with clear rectangular edges.  As the disease develops, lesions can move up the plant quickly. 

It is important to protect as much leaf area as possible, so as lesions begin to spread to the middle of the plant, treatment needs to be considered. 

As with any disease, it is important to keep in mind the ‘disease triangle’.  Three conditions must be met for a disease to continue to develop: 

  • The amount of pathogen present 
    • How much residue is on the field?  A no-till field has the potential to have much more pathogen present. 
  • The susceptibility of the host 
    • There are some hybrids that have partial resistance bred into them. 
  • A conducive environment 
    • It is important to watch the weather forecast.  In the case of GLS, if warm, humid conditions continue, we can expect the disease to continue to develop.  If the weather turns hot and dry, it is likely that development of the disease will slow down.   

If you would like help identifying this disease in your field, or need treatment options, don’t hesitate to call your local Crop Quest Agronomist. 

We are here to help you understand and manage diseases like Gray Leaf Spot effectively. 

Contact your Crop Quest Agronomist for help with this, and all your crop management decisions.

Photo Credit: Alison Robertson,