Tar spot is a fungal disease of corn which appeared in the United States in Illinois and Indiana in 2015. It was found in the northeast corner of Missouri in 2019, and is moving south and west each year. Currently, it is also confirmed in Iowa, Nebraska and Kentucky. Spots resembling tar, appear as raised, circular or elliptical spots (called stromata) on corn leaves, husks and stalks. A tan halo, also called a fish-eye lesion, may appear around the black spot. The lesion looks similar to insect frass (excrement) and other diseases like late season common or southern rust. When scratched with a fingernail, the spot does not come off of the leaf, whereas insect frass and rust pustules will. Tar spot stromata may appear on either side of the leaf, but they do not break through the leaf surface, so each individual lesion will only be on one side of the leaf.