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Collaboration Leads to Documentation: Tracking the Spread of Tar Spot on Corn in the U.S.

tar spot on corn

A new paper published in July in the Journal of Integrated Pest Management highlights tar spot on corn. First discovered in the U.S. in 2015, tar spot can cause substantial reductions in corn productivity through reduced ear weight, poor kernel development, and vivipary (the premature germination of corn kernels while they’re still on the cob). (Photo by Nathan Kleczewski, Ph.D.)

By David Coyle, Ph.D.

Editor’s Note: Here at Entomology Today, integrated pest management is a vital subject, though one usually examined through its application to insect and arthropod pests. But IPM is a framework for management of all kinds of pests, and the Entomological Society of America’s Journal of Integrated Pest Management welcomes research from beyond the confines of entomology. Today we share a look at a new case study in JIPM on corn tar spot, a disease in corn first found in the U.S. in 2015.

David Coyle, Ph.D.

David Coyle, Ph.D.

Corn is one of the most important agricultural crops in the U.S., grown on over 90 million acres of land and used primarily for animal feed and ethanol, among other uses. While production (bushels per acre) has risen steadily in recent years due to advancements in technology and production practices, price has dipped. As the profit margin is not large in farming, most farmers cannot afford yield losses due to crop pests. And yes, I know my personal and professional focus is on forest and tree pests, but my extended family still farms in southeastern Minnesota and I do keep up on the latest Midwestern farming issues. My grandfather and uncles are more than willing to share their unfiltered (and often obscenity-laced) thoughts with me on the subject of farming.

When a new disease emerges in any crop, we need to learn quickly what the disease is and what it does, as well as where it is and how it is moving. A new paper published in July in the Journal of Integrated Pest Management by Nathan Kleczewski, Ph.D. (Twitter: @ILplantdoc; email: nathank@illinois.edu), and colleagues highlights tar spot on corn. This disease, first discovered in the U.S. in 2015, can cause substantial reductions in corn productivity through reduced ear weight, poor kernel development, and vivipary (the premature germination of corn kernels while they’re still on the cob). As with many fungi, disease development is enhanced by cool, wet conditions, and a general challenge with tar spot is the lack of information on this pest, as disease incidence and severity can range widely.

tar spot map

The incidence and spread of tar spot of corn, caused by Phyllachora maydis, in the United States from 2015 to 2019. (Image originally published in Kleczewski et al 2020, Journal of Integrated Pest Management)

When tar spot started appearing in greater numbers in 2018, state extension specialists from seven states worked to share information on disease incidence in their states. In 2019, the team used EDDMapS to report county level data. These data could be uploaded and shared in real time and helped to provide a picture of a rapidly growing disease in U.S. corn. “Tracking the movement of diseases into new regions and counties is important not only for researchers, but producers,” says Kleczewski. “Documenting spread helps us learn how fast the disease moves and also provides a visual image useful in grower education. Producers in surrounding states may not have this disease on their radar when in fact, it is knocking at their back door.”

This paper is also an excellent example of how a multi-institutional team of extension personnel—both specialists and agents—can work together to document an emerging disease in a major cropping system. Plant pests do not see governmental borders, and as pest management specialists, it is important that we remember this: Diseases and insects won’t stop at the county line. This team used an electronic online mapping system to help document incidence of tar spot, and they recorded new disease spots and disseminated information to growers and county agents through social media. The importance and impact of social media and electronic resources cannot be understated and is likely to increase in the future.

David Coyle, Ph.D., is an assistant professor in the Department of Forestry and Environmental Conservation at Clemson University. Twitter: @drdavecoyle. Email: dcoyle@clemson.edu.

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