Black Tar Spot

By: Jodi Henke

Black tar spot is a fungal disease on corn that was first identified in the U.S. in 2015 and has infiltrated several states in the Corn Belt, reducing yield. Like many fungal diseases that produce spores, tar spot is carried by wind and can easily spread from field-to-field.

Nathan Kleczewski is an Extension specialist in field crops pathology at the University of Illinois. He says to scout your fields for tar spot before tasseling.

“You’re going to be looking for black structures on the foliage and sometimes on the stalks. Often times these are going to be raised and bumpy and they won’t rub off on your fingers. So, if you start to see those sorts of things, then you’re going to be dealing with tar spot,” he says. “It’s the only pathogen that forms those structures on corn.”
Warm weather, persistent rain, and high humidity during the growing season may have been the catalyst for the severity and prevalence of the disease in 2018. If you see black tar spot in your corn, it’s important to get a labeled herbicide down before the infection becomes serious.