Submitted by Wayne Flanary

Tar spot has been found in northwest Missouri in many counties. It appeared in August of last year but did not impact corn yield.

Tar spot is black lesions which can be on top or bottom of the corn leaf surface. To identify, take your thumb nail and try to scrape the black lesion off. If you cannot scrape it off, good chance it is tar spot. Southern rust in late season and insect frass can be misidentified as tar spot.

Tar spot is caused by a fungus that attacks corn which is from Central America. The symptoms are small, raised black spots that can occur on both the top and bottom of the corn leaf. The disease is found in Indiana, Iowa, Nebraska, Illinois, and Michigan along with some other states.

Tar spot is typically found during milk to late grain development. Most of what we know is from its study in Mexico and Central America.

If you are suspicious of disease that is tar spot, contact your local extension office so we can follow-up. Also, one can accurately identify this disease by submitting a sample to the MU Diagnostic Laboratory for confirmation.

For more information, contact Wayne Flanary, Fields Specialist in Agronomy, University of Missouri Extension at 816-279-1691 or cell phone 913-220-3670.