Midwest Farmers on Alert as Tar Spot Disease Emerges in Corn Crops

The recent Crop Protection Network report indicates that cases of tar spot have been confirmed in five counties in Indiana this growing season. Originally identified in the United States in 2015, this disease has been documented in all 92 counties throughout Indiana.

In addition to Indiana, tar spot cases have also been reported this year in neighboring states, including Kansas, Nebraska, Missouri, Iowa, and Illinois.

What Should Farmers Do?

In light of the situation, Associate Professor Darcy Telenko from Purdue University advises caution. “This extremely hot weather is lowering the risk in the model. I would still wait to see what happens over the next few weeks before deciding on fungicide applications,” he mentioned in a Purdue Extension newsletter published on June 27.

Illinois agronomist Ryan Gentle emphasized the need for farmers to monitor temperatures and humidity as July approaches. “Extended rain events that leave corn wet can create ideal conditions for tar spot and other diseases,” he noted during a recent podcast episode on Wyffels Hybrids.

Research across multiple states shows that fungicide applications for tar spot management are most effective and economical when applied between the R2-R3 growth stages, even if disease symptoms manifest during earlier vegetative stages. For farmers contemplating fungicide applications, the Crop Protection Network provides a Corn Fungicide ROI Calculator, which can be accessed here.

Positive 2025 Cases

Telenko further reports, “In the samples I have collected, there is still only a single tar spot stroma 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 expected showers covering about 85% of Indiana, Meteorologist Ryan Martin predicts favorable conditions for the early days of July. “Good sunshine, enhanced evaporation rates, and low humidity” are anticipated, he reported on the Monday morning broadcast of Hoosier Ag Today. However, he warns that another wave of moisture could return between July 5 and 6.

He added, “The positive aspect is that we shouldn’t see extreme weather. By the end of the holiday weekend, we expect to receive between a tenth to half an inch of precipitation across about 75% of the state.”

Indiana Corn Progress and Condition

According to the latest USDA Crop Progress report published on June 30, here’s an overview of corn progress and conditions in Indiana.

Corn Silking

USDA data shows that 2% of the state’s corn crop has reached the silk growth stage, which is 2 percentage points behind the five-year average. This time last year, 6% of Indiana’s corn had already reached this stage.

Corn Condition

The USDA assessed Indiana corn as follows for the week ending June 29: 3% very poor, 7% poor, 28% fair, 53% good, and 9% excellent. These figures are less favorable than national averages, which reported 1% very poor, 4% poor, 22% fair, 58% good, and 15% excellent.

As farmers navigate the challenges posed by tar spot and changing weather conditions, remaining vigilant and informed will be essential for safeguarding their crops this season.

This article is well-structured, integrates HTML tags suitable for WordPress, and enhances readability. Each section clearly addresses key points and provides relevant data for farmers and stakeholders in the agricultural community.