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For farmers at risk for tar spot, there are ways to manage it. But effective management starts with timely scouting and proper identification.

3 Min Read
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Submitted by Pioneer

This season, farmers may again be spotting an unwelcome guest in their corn. And its presence could have a significant impact at harvest.

Tar spot is a relatively new fungal disease impacting U.S. cornfields. In fact, its presence here wasn’t confirmed until 2015, when it was found in fields in Illinois and Indiana. Since then, it has spread rapidly across the Corn Belt, culminating in 2018 and 2021, when severe outbreaks in many Midwestern states established it as an economic concern for corn production.

As tar spot is evolving quickly, there is still much to be learned about the long-term economic impact of this disease, as well as best management practices. Farmers do have methods to help manage it now, but effective management starts with timely scouting and proper identification.  

Identifying Tar Spot

Tar spot can be identified by the fungal fruiting bodies, called ascomata, that develop on the leaf. Favorable conditions include cooler temperatures (60-70 F), high relative humidity (greater than 75%), frequent cloudy days and seven or more hours of dew at night. If fields are at risk, there is a checklist of common symptoms to watch for:

  • Tiny black spots on leaves that are oval or circular in shape

  • Leaves will develop a bumpy, uneven texture

  • Spots spread from the lowest leaves to the upper leaves

  • Spots can’t be scraped off or dissolved in water

Under favorable conditions, tar spot can spread rapidly through the corn canopy. Caused by the fungal pathogen Phyllachora maydis tar spot reduces yield potential by affecting the photosynthetic capacity of leaves and causing rapid premature biological aging or leaf senescence. In the outbreaks of 2018 and 2021, severe infestations caused yield losses as high as 50%.

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Two Tips for Better Management

Better management of tar spot begins with hybrid selection. It’s important to prioritize hybrids with genetic resistance to tar spot, as it appears to have a greater impact on symptoms and yield loss than either cultural or chemical management practices. Pioneer offers a robust lineup of hybrids with excellent tar spot scores that have performed exceptionally well in areas of infestation. It’s important to talk to local field specialists for help in determining which hybrids might perform best in your area.

Second, farmers in areas of concern should plan for fungicide applications. Several foliar fungicides, such as Aproach® Prima fungicide have proven effective in reducing tar spot symptoms and helping protect yield in corn. For fields with a history of tar spot, a second fungicide application later in the season can offer additional protection.

Farmers can find a comprehensive field guide to identifying and managing tar spot at https://www.pioneer.com/us/agronomy/tar-spot.html.

 

Aproach® Prima is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.

 

Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.™ ® Trademarks of Corteva Agriscience and its affiliated companies.

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