Tar spot of corn was found for the first time in Minnesota in late September, according to Dean Malvick, University of Minnesota Extension plant pathologist.
Malvick shared the news in a recent blog, noting that the disease was expected to move into the state, given that it was found in Iowa and Wisconsin.
“Tar spot has been found in one field in southeastern Minnesota (southern Fillmore County) where the wet summer weather has likely favored infection and spread,” he noted, adding, “This is a good time to scout for tar spot in fields that still have green leaves to get a better idea of how far this disease has spread into Minnesota.”
Although tar spot is known to occur in only one location in Minnesota, it could easily have escaped detection in other fields, Malvick said.
“In the field where the disease was found, tar spot appeared to be focused in one area that was not visible from the nearest road. Walking within the field was required to see it,” he said. “The level of infection was moderate to high on some plants. There will likely be minimal or no effect on yield because the disease appears to be limited to a small part of the field and infection likely started late in the summer. The risk of this disease is increased in the future in infected areas.”
Malvick said it can also produce fisheye symptoms, which are tan lesions with dark borders surrounding the tar spots.
Malvick said tar spot can result in significant yield losses, depending on weather, severity and timing of disease development.
“As noted, tar spot will not likely cause yield reductions in the field where it was found in Minnesota, but this find indicates that tar spot continues to spread in the Midwest,” he said. “Time will tell us how much tar spot can spread and damage corn in Minnesota.
Learn more about tar spot online. Find a map of reported distribution of tar spot in the U.S., learn more background information about tar spot and compare yield loss estimates in other states in 2018.