While corn growers had their hands full in 2025 battling Southern rust, they largely dodged a bullet from tar spot, the plant disease they’ve found to be a persistent, tough enemy since 2018.

Tar spot thrives in cool, humid conditions, and 2025 apparently removed the “cool” from the equation as temperatures across the Corn Belt were notably higher than average through the season. This robbed the disease of optimum growing conditions.

Certified crop advisor and Pioneer Field Agronomist Carl Joern, Lafayette, Ind., says the lack of a tar spot outbreak certainly wasn’t because the disease wasn’t present.

Purdue found the disease on 3-4-leaf-stage corn in the second week of June in the northern tier of counties in Indiana on a test plot designed to be a “magnet” for the disease. There, researchers use no-till, many years of corn-on-corn and plant susceptible varieties looking to find the disease — and they did,” Joern explains. 

“Generally you don’t see tar spot pre-tassel, so to find it that early leads you to think we would have been in for a bad year for the disease,” Joern says. 

Early detection of the disease (the reason for the “magnet” plot) doesn’t mean it’s all gloom and doom for the season.

“We’re getting more experienced and…