URBANA, Ill. — Tar spot, a relatively recent foliar disease to corn crops in the Midwest, has agronomists and researchers hot on its trail and concerned about possible yield losses.
“It’s hard to find a field that doesn’t have it at some level,” said Dr. Nathan Kleczewski, University of Illinois Extension plant pathologist.
Kleczewski, along with agronomists like Jim Donnelly, Asgrow/DeKalb technical agronomist for northern Illinois, have been raising the alarm about yield damage and stalk standability issues that the onslaught of tar spot could cause this year.
Tar spot, so named due to the shiny black, tar-like spots on corn leaves, is recent to the U.S. It was first spotted on corn leaves in DeKalb County, Illinois, in 2015. The fungus that causes the shiny black spots is called Phyllochora maydis. The disease tends to appear late in the growing season and, until this year, wasn’t a concern.
This year, the disease showed up early and has spread throughout cornfields in the upper Midwest.
“The disease came on fairly early and we are seeing a lot of tar-spot lesions all the way up to the top of the plant. We are not talking about one or two lesions, we are talking pretty severe infections, 30 percent or more on some of these leaves,” Kleczewski said.
Donnelly said yield losses and harvest issues are a real concern this year with the amount of tar-spot disease in fields.
“We’ve got fields where it came in so early that we are seeing severe defoliation prior to black layer. In addition, we are seeing the plants being compromised as far as standability. To fill the ear, the plant is robbing the stalks and we are seeing decreased standability,” Donnelly said.
Kleczewski, Donnelly and teams of Extension plant pathologists throughout the Midwest are working to gather leaf and plant samples of plants infected with tar spot. They are also working to rate hybrids and gather information about how tar spot impacts yields in the corn belt.
“We are trying to get our hands on as much information as we can. We’ve got projects underway and we are trying to gather data on potential yield loss, trying to look at hybrid susceptibility and we also have trials where we are looking at the effect fungicides have on tar spot,” Kleczewski said.
Kleczewski said the University of Illinois Plant Disease Clinic is collecting samples from farmers whose fields are infected with tar spot. Farmers can collect leaves, wrap them in paper or newspaper and send the samples to: Dianne Plewa, University of Illinois Plant Disease Clinic, 1102 S. Goodwin Ave., Urbana, IL 61801.
They also can contact their local Extension office to get more information about submitting leaf samples.
Kleczewski said he and his team are gathering information to find out potential variety response and yield impacts of tar spot. Farmers who would like to participate in that project can call Kleczewski at 217-300-3253 or email him at email@example.com.