Suspected corn tar spot was found the week of Sept. 18 in a dryland Michigan corn field. Michigan State University Extension is currently working on official laboratory confirmation.

In 2015, tar spot was found in the U.S. for the first time, in Indiana and Illinois. Given how late it has been found this season, there should be little impact on yield; however, researchers are working to determine if it will be a threat in the future.

Close up of corn tar spot symptoms. Photo by Martin Chilvers, MSU.

Michigan State University Extension researchers suggest keeping an eye out for this disease. Spore producing structures are produced by the tar spot fungus on the leaves, and as the name suggests, they resemble black spots of tar that feel bumpy to the touch and cannot be easily rubbed off.

To assist us in MSU’s research efforts, if you suspect tar spot, please submit a sample to MSU Diagnostic Services free of charge, courtesy of the Corn Marketing Program of Michigan. When submitting samples, be sure to indicate the location where the sample was collected.

Source: MSU Extension