Be on the Lookout for Tar Spot - A New Corn Disease

In 2019 we were concerned here in Nebraska about the development of the corn disease, tar spot in Nebraska. It was a wet year in Iowa and the Eastern Corn Belt and the disease spread from Indiana and Illinois all across Iowa. It came within one county of the eastern border of Nebraska. In 2020 it was much drier in Iowa and tar spot didn’t progress nearly as far across Iowa. If we have wet conditions this summer in the states to the east of Nebraska, be alert for tar spot to be identified in Nebraska.

Tar spot was confirmed in the United States in 2015, but not in Nebraska yet. It is characterized by black dots and “Fisheye”  rings on the leaves. There has been yield losses of up to 50% under severe infestations of this disease. Last year areas in Michigan were hit hard by tar spot. Tar spot can be controlled by fungicides and corn hybrids vary in their susceptibility. If you have corn that has raise black specks on the surface of the corn leaves that do not rub off, there is a good chance this is tar spot. If you find this in your cornfield, send in a sample to the UNL Plant and Pest Diagnostic Clinic. You can contact them at  . You can also contact me at or 402-274-4755 or 402-274-9639 and I can collect a sample for the lab.

Tar SpotGary Lesoing
Extension Educator
Nemaha County
July 2021