Tar Spot Infects Corn Crops in 14 Nebraska Counties

According to the latest Crop Protection Network map, positive cases of tar spot have been reported in 14 Nebraska counties so far this year. 

Several industry agronomists have noted, the presence of tar spot is not surprising at this point in the growing season. First reported in the Corn Belt in 2015, the disease has been confirmed in Nebraska since 2021.

Tar spot has also been recently confirmed in neighboring Iowa, Kansas, and Missouri. Illinois and Indiana also reported positive cases this month.

What Should Farmers Do

“Scouting efforts should be intensified in fields with a history of the disease or at higher risk, such as pivot-irrigated corn,” recommended a Nebraska Extension CropWatch article published June 20.

However, fungicide applications for tar spot management are not recommended at this time, the Extension experts explained. 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 article said.

“We really just need to watch the temperature and the humidity moving forward in the month of July,” Illinois based agronomist Ryan Gentle said 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 explained.

Irrigated Corn Considerations

Nebraska farmers who irrigate may want to especially pay attention scouting their corn fields. Research conducted during 2023-2024 on microclimate and disease development showed a strong relationship between irrigation and increased levels of foliar diseases in the state.

“When scouting for early disease development, it is recommended to focus scouting efforts in the innermost pivot spans,” the Extension article said.

Positive 2025 Cases

• Colfax County – 6/24
• Richardson County – 6/20
• Pawnee County – 6/20
• Johnson County – 6/20
• Otoe County – 6/20
• Lancaster County – 6/20
• Cass County – 6/20
• York County – 6/20
• Seward County – 6/17
• Polk County – 6/17
• Antelope County – 6/17
• Saunders County – 6/16
• Clay County – 6/16
• Pierce – 6/16

Nebraska Corn Progress and Condition

USDA published the latest Crop Progress report June 23.

Corn emergence is complete in Nebraska, the report said. This is slightly ahead of the 99% five-year average. However, last year 100% of the state’s corn had emerged at this time.

USDA reported 1% of the state’s corn crop has reached the silk growth stage. That’s on pace with last year at this time and slightly ahead of the five-year average.

USDA rated Nebraska corn 1% very poor, 3% poor, 26% fair, 59% good, and 11% excellent for the week that ended June 22. 

This is similar to the national averages for the week, which were reported as 2% very poor, 4% poor, 24% fair, 56% good, and 14% excellent.