University of Illinois Extension Plant Pathologist Nathan Kleczewski recently conducted an interview through the Illinois Extension news service regarding pre-season management and preparation for tar spot in 2019.

Tar spot is a foliar disease of corn that commonly occurs throughout Mexico, Central America, South America and the Caribbean. The disease was identified in the United States for the first time in 2015 in northern Illinois and Indiana. As of 2018, it had been confirmed in Iowa, Michigan, Wisconsin, Ohio. and Florida. The whole interview can be found here.

Some quick points from the interview:

  • Tar spot likes cooler, humid conditions (60-70 degrees Fahrenheit overnight)
  • Typical tar spot appearance has been late in the growing season, after most grain has been filled. Last year in Illinois, the disease appeared early and caused between 10-40/50 bu/acre yield loss.
  • There are no fully resistant hybrids for tar spot, but some hybrids are more tolerant of the disease than others. Check with your seed supplier on tolerance levels. Damon Smith, out of the University of Wisconsin-Madison, published hybrid performance trials in regards to tar spot severity. His results can be found here.
  • Fungicide applications can be effective, but it is all about timing. Scouting is imperative. When the disease starts appearing is the key. If the disease is present before the tasseling/R1 stage, an application could provide results.

For resources on tar spot, visit the Crop Protection Network, which recently posted a free management guide for the disease, this year.