Understanding spread and development of corn tar spot in Minnesota

photograph of corn tar spot on a corn plant leaf

Tar spot of corn on a corn leaf



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 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?

Practical implications

The results of this work will provide the information needed to understand and effectively manage P. maydis, filling the large gaps of information that exist about this disease. By understanding key variables particular to Minnesota, land managers will be able to more accurately assess risk and develop durable disease management practices for tar spot of corn.

Research team

Dean Malvick | principal investigator

José E. Solórzano | PhD student

Crystal Floyd | researcher


Lab or other website



Collaborating organizations

Midwestern Tar Spot Working Group