Higher-than-normal rainfall in the corn belt is increasing disease risk as the corn crop enters the reproductive stage. The latest Crop Protection Network Map shows positive cases of tar spot reported across much of the corn belt. This includes:

  • Wisconsin
  • Illinois
  • Indiana
  • Iowa, 26 counties
  • Missouri
  • Nebraska, 19 counties
  • Michigan
  • Pennsylvania
  • New York

Tar spot has progressed across the Corn Belt over the past eight years. It appears as black spots that do not rub or wash off and has the potential to decimate corn yields. Iowa State University Agronomist Rebecca Vittetoe advises farmers to scout their fields.

Corrective action to minimize the impact of tar spot includes timed fungicide applications. Iowa Extension Agronomist Gentry Sorenson reports the crop in northwest Iowa is late-stage vegetative to R2. That is the right time to target tar spot with fungicide. Multi-state fungicide research has shown that applications for tar spot are most effective between R2-R3.

A Corn Fungicide ROI Calculator is available from the Crop Protection Network.

Read more about the spread of tar spot across the Corn Belt here.