Corn tar spot found in Michigan

Corn tar spot was recently discovered in Michigan for the first time. Growers should keep an eye out for this new disease as we approach harvest.

Tar spot on corn. All photos: Martin Chilvers, MSU.

Tar spot on corn. All photos: Martin Chilvers, MSU.

Suspected corn tar spot was found last week (the week of Sept. 18, 2016) in a dryland Michigan corn field. We are 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, we need to determine if it will be a threat in the future.

Michigan State University Extension suggests keeping an eye out for this disease as we approach harvest. 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 our 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.

Martin Chilvers’ research is partially supported by the Corn Marketing Program of Michigan.

Carbon dioxide injury to apples Corn tar spot symptoms

Close up of corn tar spot symptoms.

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