Distribution, risks, and management of corn tar spot

photograph of corn tar spot pathogen on a corn leaf

Corn tar spot on a corn plant leaf

Photo by Dean Malvick


Corn tar spot is a leaf disease caused by the fungus Phyllachora maydis. It produces black spots on leaves, and can cause significant yield loss for corn, the most widely grown crop in Minnesota. Yield loss can exceed 40%. It was first detected in the United States in 2015 in Illinois and Indiana, and has since spread to multiple states in the Midwest, including southeastern Minnesota where it has been confirmed in 12 counties. Currently, there is limited information about the distribution, biology, and management of corn tar spot.

Research questions

  • What is the distribution of corn tar spot, and how established is it?
  • How do we detect corn tar spot? 
  • How will corn tar spot respond to future weather conditions? 
  • What are our management options for corn tar spot, and how effective are they? 

Practical implications

This project will document distribution of corn tar spot over time. It will also clarify the host range of the tar spot pathogen to determine if common plant species can harbor it. Methods to detect tar spot will be validated and developed as needed. 

Lastly, pilot studies will be conducted to evaluate fungicides and corn hybrids to manage tar spot in Minnesota environments.


News and media

Research team

Dean Malvick | principal investigator

José E Solórzano | PhD student


Collaborating organizations

National Institute of Food and Agriculture (USDA)

Minnesota Department of Agriculture

University of Minnesota Plant Disease Clinic