Proper Crop Nutrition to Combat Tar Spot
February 26, 2025 As winter turns to spring, ag retailers and their grower-customers are gearing up for the 2025 growing season. And for many corn growers, the risk of diseases – particularly tar spot – will also be on their minds.
Caused by the fungus Phyllachora maydis, tar spot is not a new disease. In fact, the first documented cases of it in corn date back more than 100 years to 1904. But until approximately 2015, it had never been a major crop disease in the U.S. Since then, however, tar spot has steadily spread across much of the Corn Belt. And it can be devastating for corn growers, with infestations leading to up to 50% yield reductions.
“There’s lots we don’t know about this disease,” said Travis Coleman, Southern Indiana Agronomist for Beck’s Hybrids, speaking at the 2025 National Farm Machinery Show in mid-February. “As of today, the ag industry doesn’t have a good answer for controlling tar spot.”
Significantly, said Coleman, 2024 was a very nasty year for tar spot infestations across the country, particularly in the Hoosier State. “Last year, all 92 counties in Indiana saw tar spot in corn fields,” he said.
Why was 2024 so bad for tar spot infestations? According to Coleman, the weather during the year across much of the Midwest made conditions ideal for its spread.
“Tar spot does best in temperature ranges from 60 to 70 degrees and humidity greater than 75%,” he said. “2024 was very hot and humid, being the second warmest year on record. Also, tar spot overwinters in residue, and there was a lot of this leftover in fields last year.”
To combat tar spot, Coleman made a few suggestions. One was to reduce the number of corn plant populations per acre to allow for better airflow through crop rows, reducing humidity levels. The other was to use different kinds of crop nutrients to improve a plant’s ability to fight back against the fungus.
Loading ...“If you are looking for a silver bullet for tar spot, you aren’t going to find it,” he said. “But proper fertility can be a way to manage tar spot. Products like sulfur can help, as can certain micronutrients such as copper, zinc, and boron. Consider using these this spring.”
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