Tracking Tar Spot: Protecting Minnesota's Corn
New invasive species Corn Tar Spot may be Minnesota corn farmers’ newest challenge. Where does it come from? How fast will it spread? What helps it develop? Researchers at the Minnesota Invasive Terrestrial Plants and Pests Center are on the case.
February 12, 2021
by MAGGIE NESBIT | Communications Intern, MITPPC
Tar spot, caused by the fungus Phyllachora maydis, may be Minnesota corn farmers’ newest challenge. Where does it come from? How fast will it spread? What helps it develop? These are questions that plant pathologist Dean Malvick is looking to answer in a new project funded by the Minnesota Invasive Terrestrial Plants and Pests Center that will begin in early summer 2021.
“I think many farmers, crop consultants, and people in agribusiness in southeastern Minnesota now know that this is something they really need to be watching for,” said Malvick.
Tar spot is a fungal disease of corn leaves, its origins tracing back to Latin America, including southern Mexico, Central America, northern South America, and Puerto Rico. It was first discovered in the United States in 2015, making its first known appearance in north central Indiana and Illinois. It produces black spots on leaves, and can cause yield losses of up to 40% for corn, the most widely grown crop in Minnesota.
In Latin America, corn tar spot seems to involve two species of fungi. However, it is likely that only one of those species made it to the United States. Because of this, plant pathologists initially thought the risk might be low here compared to other regions. However, it appears that Phyllachora maydis can cause significant damage to corn yields on its own in the U.S.
In late 2019, the discovery of tar spot south of Rochester, Minnesota set off alarm bells. Since its first appearance in the state, it has been confirmed to spread to a total of 12 counties.
“I think it was interesting to a lot of folks that it has spread and became as common in some areas as it did. I think it really opened up a lot of eyes that this is something that we need to pay attention to,” said Malvick.
Malvick and his team want to better understand its distribution through surveys and sampling, leading to a better understanding of how and where it’s spreading. He will be collaborating with crop consultants and agronomists from seed companies and others around the state in order to collect samples to analyze.
“Some positive outcomes will include having a better understanding of factors that contribute to its development as well as where this disease poses the greatest threat ,” said Malvick on what he hopes will come of this project.
The team is also hoping to understand the weather and climatic factors that relate to its development, as weather has proven to be a large factor. Although the disease has not been confirmed to cause yield loss in Minnesota yet, evidence shows it reached levels that would have likely caused loss had it developed a few weeks earlier. This was due to a period of dryness in the state that occurred in late July and early August. Dry weather suppresses development of the disease. Malvick points out that if the Minnesota summer had been wetter, tar spot would have been more prevalent and would have likely posed bigger problems for corn growers.
Another factor of this project is determining what other plants in Minnesota tar spot may affect. Primarily, this fungus is a pathogen of corn, but previous research has shown that closely related fungi can infect species of grasses. It’s not well understood which other plant species the corn tar spot pathogen infects besides corn, and the team is hoping to take a closer look.
This project also includes pilot studies on methods of management and detection. Spraying fungicides is an important part of management of tar spot in other states, but Malvick and his team are looking to hone in on how well fungicides work to manage the disease in Minnesota.
“Every place is different. So, we need to get some data from Minnesota. We'd also like more information on corn hybrids adapted to Minnesota and how susceptible they are to this disease. We also hope to develop and improve experimental methods and validate those that others are working on,” Malvick said.
Because this disease is new to Minnesota, little is known about its basic functions and development here. This situation creates both an advantage and a disadvantage to Malvick: “If the methods were all developed, it would make parts of this project easier. On the other hand, if we can get a jump on understanding and managing this disease earlier, we might have an advantage in managing and reducing its impact in the state.”
Malvick will be communicating with farmers and agribusiness and Extension educators throughout this two-year project to keep them updated on the team’s findings. He will also be presenting findings at scientific meetings and plans on publishing significant results and using what he discovers in his teaching.
“I think it’s really useful to both manage the disease in the near term and build more knowledge to improve management understanding in the long term,” he said.
Learn more about this project here. This work is funded by the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources.