First tar spot detection confirmed in Indiana for 2026

WEST LAFAYETTE, Ind. — Tar spot has been detected in Indiana for the first time this growing season in Randolph County.

“Questions about tar spot management were already beginning to surface as corn planting nears completion across Indiana,” said Darcy Telenko, Purdue Extension field crop pathologist.

Drawing from eight seasons of tar spot observations, research and field experience, she shared tips to help farmers stay ahead of tar spot.

“Every season is different,” she said. “Tar spot development is driven by the disease triangle: susceptible host, pathogen presence and favorable environmental conditions.

“Weather patterns through June are especially important and often determine when disease becomes established in the lower canopy.”

Darcy Telenko — Telenko (Purdue Extension photo/Laurie Iten)

Telenko encouraged farmers to scout early and scout often.

“Begin monitoring fields when corn reaches V7-V8, focusing on the lower canopy for the first tar spot stromata,” she said.

“To distinguish tar spot from insect frass (or false tar spot), try rubbing the spot and inspect the underside of the leaf for a corresponding lesion directly beneath the upper-canopy spot.

“Early detection is critical. Once disease severity reaches 5% or greater in the upper canopy, fungicides are unlikely to effectively slow disease progression. Follow disease monitoring maps to track first detections in your area.”