Scouting for tar spot. Credit: Domini Brown
Background
Tar spot of corn is an emerging plant disease in the United States caused by the invasive pathogen, Phyllachora maydis. It has caused significant yield loss across the country, estimated at 230 million bushels in 2021.
The pathogen was first found in Minnesota in 2019 and the distribution has since increased to 23 counties. Its establishment in Minnesota is not well understood. Management options to mitigate the loss of corn production are currently limited.
This project team seeks to build on previous research, and generate information about tar spot of corn to better enable risk assessment, mitigation, and management. They will build on previous work in which they collected and studied other Phyllachora species found on different plants in the state. Specifically, researchers will investigate the distribution, host range, ideal growing conditions, and determine key factors that influence disease development of P. maydis in Minnesota.
Research questions
- What is the distribution, host range, and dispersal of P. maydis in Minnesota?
- What are the conditions and pathogen characteristics that favor development of P. maydis in Minnesota?
- What is the best inoculation method to enable research in field and greenhouse studies?
- What key factors influence disease development and efficacy of management practices?
Outcomes
During this project, researchers:
- Documented and confirmed the spread of corn tar spot in 55 counties in Minnesota, representing most corn producing areas of the state. The expanded range indicates that disease scouting is needed in most areas for managing this problem.
- Improved a DNA-based qPCR assay to detect P. maydis in collaboration with other colleagues.
- Confirmed that in Minnesota, the conditions needed for the development of tar spot are not as reported in most literature. Tar spot can develop and spread in low rainfall conditions with moderate to low humidity. It is still unknown the conditions for severe infection.
- Determined that the Phyllachora species can infect grasses, however the species found in grasses do not infect corn.
- Discovered that P. maydis can infect eastern gammgrass and teosinte, which establishes for the first time that the host range of the pathogen includes additional plant species.
- Confirmed that foliar-applied fungicides can effectively reduce tar spot in Minnesota environments.
- Enhanced knowledge of inoculation, infection, tar spot development, disease risk, and management of tar spot in field environments.
Publications
- Foliar inoculation of Phyllachora maydis into corn induces infection and local spread in field environments (Plant Disease, 2024); author's manuscript available to read for free
Outreach
- Crop Pest Management Short Course, 2024
- UMN Extension Research Updates (Rochester, Waseca, Lamberton, Wilmar, Crookston), 2025
- Meeting with crop consultants in Morton, MN, 2025
- South Dakota State University regional webinar, 2025
- Meeting with Corteva plant pathologists, 2025
- Strategic Farming webinar, UMN Extension, 2025
- Extension program meetings across Minnesota, 2025
- Crop Input Seminar in Hutchinson, MN, 2025
- Research Update Meetings in Waseca, Lamberton, Wilmar, and Farmington, MN, 2026
News and media
- Bursting the fungal menace of corn tar spot wide open - MITPPC
- Tar spot update: Experts answer questions after tough year - Indiana Prairie Farmer
- José Solórzano profile - Dept. of Plant Pathology
- UMN scientists make breakthrough in tar spot pathogen research - MN Daily
- Breakthrough on tar spot pathogen enables field research - UMN News
- Studying tar spot just got easier - FarmProgress
- Identifying the host range of the fungus Phyllachora maydis, the corn tar spot pathogen - Minnesota Mycological Society
- Uncovering clues to corn tar spot, a complex and cold-hardy fungus - MITPPC