Tar spot symptoms include tar-like spots on the leaf surface.

The corn disease tar spot was back in abundance this season and may present even more of an issue in 2020. As of October 31, there are 270 counties across the U.S. with confirmed reports of tar spot, including a first time sighting in MN.

Researchers with The Ohio State University Extension say the disease appeared late in the season after R4, but was found in more fields and with greater severity than last year. According to Iowa State University researchers, with every 10% increase in disease severity, tar spot can cause a 10 to 15 bu/A yield loss. It’s possible corn with tar spot infection could easily experience 30 to 40 bu/A in yield losses¹.

While you may not have spotted it in your fields this year, tar spot is able to overwinter and survive cold temperatures. Although only approximately 20 to 25% of spores will survive until spring, tar spot is capable of producing millions of spores under the right conditions, so only a few overwintering spores are needed to cause significant damage. Due to the high disease pressure in 2019, there is an increased risk of tar spot reappearing and spreading to more regions next season.

Tar spot has a latent period of up to 14 days, so corn will be infected before the dark, tar-like spots appear on the leaf. It’s an aggressive disease that’s difficult to manage once it’s gotten a good start in a field.

Stay vigilant and don’t fall behind in 2020. Consider planning for a preventive fungicide application next season to protect your profit potential.

With one of the highest-performing SDHI mode of action available, Miravis® Neo fungicide sets a new standard in its class for broad-spectrum disease control, including tar spot. Miravis Neo also provides plant-health benefits to help corn stay healthier longer, helping the plant reach full yield potential.

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¹CornPro 3.4 Iowa State University.