Tar Spot of Corn

PATHOGEN FACTS

Tar spot, caused by the fungal pathogen Phyllachora maydis, is a relatively new foliar disease of corn in the United States, first appearing in Illinois and Indiana in 2015 and subsequently spreading through much of the Corn Belt.
Look for tar spot to develop during cool temperatures (60-70 ºF, 16-20 ºC), high relative humidity (>75%), frequent cloudy days, and 7+ hours of dew at night.
Tar spot reduces yield by reducing the photosynthetic capacity of leaves and causing rapid premature leaf senescence.