Tar Spot Infects Corn Crops in 5 Indiana Counties

The latest Crop Protection Network map shows positive cases of tar spot have been reported in five Indiana counties so far this growing season. First reported in the U.S. in 2015, there is a history of the disease in all 92 Indiana counties.

Tar spot has also been confirmed in Kansas, Nebraska, Missouri, Iowa, and Illinois this year.

What Should Farmers Do?

“This extremely hot weather is lowering the risk in the model. I would still wait to see what happens the next few weeks before pulling the fungicide trigger,” advised Associate Professor of Botany and Plant Pathology Darcy Telenko in a Purdue Extension newsletter published June 27.

Illinois based agronomist Ryan Gentle stressed the importance of watching temperatures and humidity levels as the calendar turns to July on a recent Wyffels Hybrids podcast episode. Large rain events where the corn stays wet for a long time can create ideal conditions for tar spot and other diseases to take off, he said.

Multi-state fungicide research results show that applications made for tar spot management are most effective and economical when made between R2-R3, even when disease developed during early vegetative stages.

The Crop Protection Network offers a Corn Fungicide ROI Calculator for farmers weighing a fungicide application. Access the calculator and read about the tool’s supporting research here: cropprotectionnetwork.org/fungicide-roi-calculator

Positive 2025 Cases

Telenko notes, “In the samples I have found it is still only a single tar spot stromata on a lower leaf in V8-V10 corn.”

• Porter County – June 11
• Tipton County – June 24
• La Porte County – June 25
• Starke County – June 25
• Cass County – June 26

Indiana Weather Forecast

Following Monday showers that were expected to cover about 85% of the state, Tuesday, Wednesday, and Thursday are “looking pretty doggone nice,” said Meteorologist Ryan Martin on the Monday morning broadcast of Hoosier Ag Today. He expects, “good sunshine, good evaporation rates, low humidity” through the 4th of July holiday in Indiana. Overnight on July 5 into July 6 is “when we see our next little wave of moisture come through,” Martin said.

“The good news is it’s not over the top. I think we’re looking at finishing the holiday weekend with a tenth to half an inch across about 75% of the Hoosier state,” he said. Following the holiday weekend, warmer and more humid air will try to come back and could create some instability, he added.

Indiana Corn Progress and Condition

USDA published the latest Crop Progress report June 30. Here’s a closer look at corn progress and conditions across Indiana.

Corn Silking

USDA reported 2% of the state’s corn crop has reached the silk growth stage. That is 2 percentage points behind the five-year average. Last year at this time 6% of Indiana’s corn had reached the silk growth stage.

Corn Condition

USDA rated Indiana corn 3% very poor, 7% poor, 28% fair, 53% good, and 9% excellent for the week that ended June 29.

This is worse than the national averages for the wheel, which were reported as 1% very poor, 4% poor, 22% fair, 58% good, and 15% excellent.