Tar Spot Spreads Across Ohio's Corn Belt

The Ohio Department of Agriculture has confirmed its first cases of tar spot for the 2026 growing season, with infections detected in seven counties. The disease has been identified in Clark, Darke, Ross, Fayette, Wyandot, Morrow, and Pickaway counties.

The findings are significant because tar spot can rapidly reduce photosynthetic leaf area during grain fill, potentially affecting yield when environmental conditions favor disease development.

Tar spot was first identified in Ohio in 2018, and since then, 49 of the state's 88 counties have reported the disease at least once. The disease has also been confirmed in several other states across the Corn Belt, including Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, New York, Virginia, and Wisconsin.

Field agronomists report that Ohio's corn crop remains in generally good condition, despite localized drought in parts of southern Ohio. However, increasing humidity and longer periods of leaf wetness are creating more favorable conditions for foliar diseases, including tar spot, gray leaf spot, and northern corn leaf blight.