Iowa Corn: Tar Spot Samples Needed for Research

Close up of tar spot on corn leaf. Photo: Martin Chilvers, Michigan State University

The University of Illinois, Urbana, is seeking assistance from its friendly neighbor to the west, the corn-state of Iowa, in locating samples of tar spot in corn. This is part of the university’s new research project investigating the genetic variability of the tar spot pathogen.

Tar spot symptoms are small, black raised spots — that can be circular or oval — and may appear on one or both sides of leaves, leaf sheaths and husks. These spots can be found on both healthy green leaves and dying (brown) tissue. The black spots are surrounded by a tan or brown halo, which can be especially obvious on healthy leaves.

Tar spot of corn is a new corn disease first identified in the U.S. in 2015 in Illinois and Indiana. It has since been confirmed in Iowa, Michigan, Wisconsin and Florida. Researchers haven’t seen data that tar spot in corn directly causes yield loss, however, in research conducted in Mexico and South America, the fungus Monographella maydis follows the tar spot fungus and does cause yield loss.

If you have, or believe that you have a sample of corn tar spot, the University of Illinois would be greatly appreciative of your assistance in helping them with their project. If interested, please collect several leaves showing the symptoms and send them in using this form. Please wrap the leaves in newspaper or dry paper towels and ship in a large envelope. Please ship the samples early in the week. If sending samples from multiple locations, please label them and provide the appropriate information to the form.

Here is an additional permit that will allow the university to receive out of state samples, that should be included in the sample package.

Should you have any question, please contact Diane Plewa, of the University of Illinois Plant Clinic.

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“If anyone in the state has any samples of tar spot, it would be great if they could assist the University of Illinois in their research,” said Extension Plant Pathologist and Director of the Iowa State University Integrated Pest Management (IPM) program Daren Mueller.

“University collaboration is important to the overall mission of IPM, as it allows us to find better, more efficient solutions to control pests. With tar spot in corn having a presence in Iowa, this research could play a critical role in helping us to be prepared in the event that the pathogen becomes a dominant factor in crop production.”


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